source: vbox/trunk/src/VBox/ExtPacks/VBoxDTrace/onnv/uts/common/dtrace/dcpc.c@ 53703

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#include <sys/errno.h>
#include <sys/cpuvar.h>
#include <sys/stat.h>
#include <sys/modctl.h>
#include <sys/cmn_err.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
#include <sys/ksynch.h>
#include <sys/conf.h>
#include <sys/kmem.h>
#include <sys/kcpc.h>
#include <sys/cap_util.h>
#include <sys/cpc_pcbe.h>
#include <sys/cpc_impl.h>
#include <sys/dtrace_impl.h>

/*
 * DTrace CPU Performance Counter Provider
 * ---------------------------------------
 *
 * The DTrace cpc provider allows DTrace consumers to access the CPU
 * performance counter overflow mechanism of a CPU. The configuration
 * presented in a probe specification is programmed into the performance
 * counter hardware of all available CPUs on a system. Programming the
 * hardware causes a counter on each CPU to begin counting events of the
 * given type. When the specified number of events have occurred, an overflow
 * interrupt will be generated and the probe is fired.
 *
 * The required configuration for the performance counter is encoded into
 * the probe specification and this includes the performance counter event
 * name, processor mode, overflow rate and an optional unit mask.
 *
 * Most processors provide several counters (PICs) which can count all or a
 * subset of the events available for a given CPU. However, when overflow
 * profiling is being used, not all CPUs can detect which counter generated the
 * overflow interrupt. In this case we cannot reliably determine which counter
 * overflowed and we therefore only allow such CPUs to configure one event at
 * a time. Processors that can determine the counter which overflowed are
 * allowed to program as many events at one time as possible (in theory up to
 * the number of instrumentation counters supported by that platform).
 * Therefore, multiple consumers can enable multiple probes at the same time
 * on such platforms. Platforms which cannot determine the source of an
 * overflow interrupt are only allowed to program a single event at one time.
 *
 * The performance counter hardware is made available to consumers on a
 * first-come, first-served basis. Only a finite amount of hardware resource
 * is available and, while we make every attempt to accomodate requests from
 * consumers, we must deny requests when hardware resources have been exhausted.
 * A consumer will fail to enable probes when resources are currently in use.
 *
 * The cpc provider contends for shared hardware resources along with other
 * consumers of the kernel CPU performance counter subsystem (e.g. cpustat(1M)).
 * Only one such consumer can use the performance counters at any one time and
 * counters are made available on a first-come, first-served basis. As with
 * cpustat, the cpc provider has priority over per-LWP libcpc usage (e.g.
 * cputrack(1)). Invoking the cpc provider will cause all existing per-LWP
 * counter contexts to be invalidated.
 */

typedef struct dcpc_probe {
        char            dcpc_event_name[CPC_MAX_EVENT_LEN];
        int             dcpc_flag;      /* flags (USER/SYS) */
        uint32_t        dcpc_ovfval;    /* overflow value */
        int64_t         dcpc_umask;     /* umask/emask for this event */
        int             dcpc_picno;     /* pic this event is programmed in */
        int             dcpc_enabled;   /* probe is actually enabled? */
        int             dcpc_disabling; /* probe is currently being disabled */
        dtrace_id_t     dcpc_id;        /* probeid this request is enabling */
        int             dcpc_actv_req_idx;      /* idx into dcpc_actv_reqs[] */
} dcpc_probe_t;

static dev_info_t                       *dcpc_devi;
static dtrace_provider_id_t             dcpc_pid;
static dcpc_probe_t                     **dcpc_actv_reqs;
static uint32_t                         dcpc_enablings = 0;
static int                              dcpc_ovf_mask = 0;
static int                              dcpc_mult_ovf_cap = 0;
static int                              dcpc_mask_type = 0;

/*
 * When the dcpc provider is loaded, dcpc_min_overflow is set to either
 * DCPC_MIN_OVF_DEFAULT or the value that dcpc-min-overflow is set to in
 * the dcpc.conf file. Decrease this value to set probes with smaller
 * overflow values. Remember that very small values could render a system
 * unusable with frequently occurring events.
 */
#define DCPC_MIN_OVF_DEFAULT            5000
static uint32_t                         dcpc_min_overflow;

static int dcpc_aframes = 0;    /* override for artificial frame setting */
#if defined(__x86)
#define DCPC_ARTIFICIAL_FRAMES  8
#elif defined(__sparc)
#define DCPC_ARTIFICIAL_FRAMES  2
#endif

/*
 * Called from the platform overflow interrupt handler. 'bitmap' is a mask
 * which contains the pic(s) that have overflowed.
 */
static void
dcpc_fire(uint64_t bitmap)
{
        int i;

        /*
         * No counter was marked as overflowing. Shout about it and get out.
         */
        if ((bitmap & dcpc_ovf_mask) == 0) {
                cmn_err(CE_NOTE, "dcpc_fire: no counter overflow found\n");
                return;
        }

        /*
         * This is the common case of a processor that doesn't support
         * multiple overflow events. Such systems are only allowed a single
         * enabling and therefore we just look for the first entry in
         * the active request array.
         */
        if (!dcpc_mult_ovf_cap) {
                for (i = 0; i < cpc_ncounters; i++) {
                        if (dcpc_actv_reqs[i] != NULL) {
                                dtrace_probe(dcpc_actv_reqs[i]->dcpc_id,
                                    CPU->cpu_cpcprofile_pc,
                                    CPU->cpu_cpcprofile_upc, 0, 0, 0);
                                return;
                        }
                }
                return;
        }

        /*
         * This is a processor capable of handling multiple overflow events.
         * Iterate over the array of active requests and locate the counters
         * that overflowed (note: it is possible for more than one counter to
         * have overflowed at the same time).
         */
        for (i = 0; i < cpc_ncounters; i++) {
                if (dcpc_actv_reqs[i] != NULL &&
                    (bitmap & (1ULL << dcpc_actv_reqs[i]->dcpc_picno))) {
                        dtrace_probe(dcpc_actv_reqs[i]->dcpc_id,
                            CPU->cpu_cpcprofile_pc,
                            CPU->cpu_cpcprofile_upc, 0, 0, 0);
                }
        }
}

static void
dcpc_create_probe(dtrace_provider_id_t id, const char *probename,
    char *eventname, int64_t umask, uint32_t ovfval, char flag)
{
        dcpc_probe_t *pp;
        int nr_frames = DCPC_ARTIFICIAL_FRAMES + dtrace_mach_aframes();

        if (dcpc_aframes)
                nr_frames = dcpc_aframes;

        if (dtrace_probe_lookup(id, NULL, NULL, probename) != 0)
                return;

        pp = kmem_zalloc(sizeof (dcpc_probe_t), KM_SLEEP);
        (void) strncpy(pp->dcpc_event_name, eventname,
            sizeof (pp->dcpc_event_name) - 1);
        pp->dcpc_event_name[sizeof (pp->dcpc_event_name) - 1] = '\0';
        pp->dcpc_flag = flag | CPC_OVF_NOTIFY_EMT;
        pp->dcpc_ovfval = ovfval;
        pp->dcpc_umask = umask;
        pp->dcpc_actv_req_idx = pp->dcpc_picno = pp->dcpc_disabling = -1;

        pp->dcpc_id = dtrace_probe_create(id, NULL, NULL, probename,
            nr_frames, pp);
}

/*ARGSUSED*/
static void
dcpc_provide(void *arg, const dtrace_probedesc_t *desc)
{
        /*
         * The format of a probe is:
         *
         *      event_name-mode-{optional_umask}-overflow_rate
         * e.g.
         *      DC_refill_from_system-user-0x1e-50000, or,
         *      DC_refill_from_system-all-10000
         *
         */
        char *str, *end, *p;
        int i, flag = 0;
        char event[CPC_MAX_EVENT_LEN];
        long umask = -1, val = 0;
        size_t evlen, len;

        /*
         * The 'cpc' provider offers no probes by default.
         */
        if (desc == NULL)
                return;

        len = strlen(desc->dtpd_name);
        p = str = kmem_alloc(len + 1, KM_SLEEP);
        (void) strcpy(str, desc->dtpd_name);

        /*
         * We have a poor man's strtok() going on here. Replace any hyphens
         * in the the probe name with NULL characters in order to make it
         * easy to parse the string with regular string functions.
         */
        for (i = 0; i < len; i++) {
                if (str[i] == '-')
                        str[i] = '\0';
        }

        /*
         * The first part of the string must be either a platform event
         * name or a generic event name.
         */
        evlen = strlen(p);
        (void) strncpy(event, p, CPC_MAX_EVENT_LEN - 1);
        event[CPC_MAX_EVENT_LEN - 1] = '\0';

        /*
         * The next part of the name is the mode specification. Valid
         * settings are "user", "kernel" or "all".
         */
        p += evlen + 1;

        if (strcmp(p, "user") == 0)
                flag |= CPC_COUNT_USER;
        else if (strcmp(p, "kernel") == 0)
                flag |= CPC_COUNT_SYSTEM;
        else if (strcmp(p, "all") == 0)
                flag |= CPC_COUNT_USER | CPC_COUNT_SYSTEM;
        else
                goto err;

        /*
         * Next we either have a mask specification followed by an overflow
         * rate or just an overflow rate on its own.
         */
        p += strlen(p) + 1;
        if (p[0] == '0' && (p[1] == 'x' || p[1] == 'X')) {
                /*
                 * A unit mask can only be specified if:
                 * 1) this performance counter back end supports masks.
                 * 2) the specified event is platform specific.
                 * 3) a valid hex number is converted.
                 * 4) no extraneous characters follow the mask specification.
                 */
                if (dcpc_mask_type != 0 && strncmp(event, "PAPI", 4) != 0 &&
                    ddi_strtol(p, &end, 16, &umask) == 0 &&
                    end == p + strlen(p)) {
                        p += strlen(p) + 1;
                } else {
                        goto err;
                }
        }

        /*
         * This final part must be an overflow value which has to be greater
         * than the minimum permissible overflow rate.
         */
        if ((ddi_strtol(p, &end, 10, &val) != 0) || end != p + strlen(p) ||
            val < dcpc_min_overflow)
                goto err;

        /*
         * Validate the event and create the probe.
         */
        for (i = 0; i < cpc_ncounters; i++) {
                char *events, *cp, *p, *end;
                int found = 0, j;
                size_t llen;

                if ((events = kcpc_list_events(i)) == NULL)
                        goto err;

                llen = strlen(events);
                p = cp = ddi_strdup(events, KM_NOSLEEP);
                end = cp + llen;

                for (j = 0; j < llen; j++) {
                        if (cp[j] == ',')
                                cp[j] = '\0';
                }

                while (p < end && found == 0) {
                        if (strcmp(p, event) == 0) {
                                dcpc_create_probe(dcpc_pid, desc->dtpd_name,
                                    event, umask, (uint32_t)val, flag);
                                found = 1;
                        }
                        p += strlen(p) + 1;
                }
                kmem_free(cp, llen + 1);

                if (found)
                        break;
        }

err:
        kmem_free(str, len + 1);
}

/*ARGSUSED*/
static void
dcpc_destroy(void *arg, dtrace_id_t id, void *parg)
{
        dcpc_probe_t *pp = parg;

        ASSERT(pp->dcpc_enabled == 0);
        kmem_free(pp, sizeof (dcpc_probe_t));
}

/*ARGSUSED*/
static int
dcpc_usermode(void *arg, dtrace_id_t id, void *parg)
{
        return (CPU->cpu_cpcprofile_pc == 0);
}

static void
dcpc_populate_set(cpu_t *c, dcpc_probe_t *pp, kcpc_set_t *set, int reqno)
{
        kcpc_set_t *oset;
        int i;

        (void) strncpy(set->ks_req[reqno].kr_event, pp->dcpc_event_name,
            CPC_MAX_EVENT_LEN);
        set->ks_req[reqno].kr_config = NULL;
        set->ks_req[reqno].kr_index = reqno;
        set->ks_req[reqno].kr_picnum = -1;
        set->ks_req[reqno].kr_flags =  pp->dcpc_flag;

        /*
         * If a unit mask has been specified then detect which attribute
         * the platform needs. For now, it's either "umask" or "emask".
         */
        if (pp->dcpc_umask >= 0) {
                set->ks_req[reqno].kr_attr =
                    kmem_zalloc(sizeof (kcpc_attr_t), KM_SLEEP);
                set->ks_req[reqno].kr_nattrs = 1;
                if (dcpc_mask_type & DCPC_UMASK)
                        (void) strncpy(set->ks_req[reqno].kr_attr->ka_name,
                            "umask", 5);
                else
                        (void) strncpy(set->ks_req[reqno].kr_attr->ka_name,
                            "emask", 5);
                set->ks_req[reqno].kr_attr->ka_val = pp->dcpc_umask;
        } else {
                set->ks_req[reqno].kr_attr = NULL;
                set->ks_req[reqno].kr_nattrs = 0;
        }

        /*
         * If this probe is enabled, obtain its current countdown value
         * and use that. The CPUs cpc context might not exist yet if we
         * are dealing with a CPU that is just coming online.
         */
        if (pp->dcpc_enabled && (c->cpu_cpc_ctx != NULL)) {
                oset = c->cpu_cpc_ctx->kc_set;

                for (i = 0; i < oset->ks_nreqs; i++) {
                        if (strcmp(oset->ks_req[i].kr_event,
                            set->ks_req[reqno].kr_event) == 0) {
                                set->ks_req[reqno].kr_preset =
                                    *(oset->ks_req[i].kr_data);
                        }
                }
        } else {
                set->ks_req[reqno].kr_preset = UINT64_MAX - pp->dcpc_ovfval;
        }

        set->ks_nreqs++;
}


/*
 * Create a fresh request set for the enablings represented in the
 * 'dcpc_actv_reqs' array which contains the probes we want to be
 * in the set. This can be called for several reasons:
 *
 * 1)   We are on a single or multi overflow platform and we have no
 *      current events so we can just create the set and initialize it.
 * 2)   We are on a multi-overflow platform and we already have one or
 *      more existing events and we are adding a new enabling. Create a
 *      new set and copy old requests in and then add the new request.
 * 3)   We are on a multi-overflow platform and we have just removed an
 *      enabling but we still have enablings whch are valid. Create a new
 *      set and copy in still valid requests.
 */
static kcpc_set_t *
dcpc_create_set(cpu_t *c)
{
        int i, reqno = 0;
        int active_requests = 0;
        kcpc_set_t *set;

        /*
         * First get a count of the number of currently active requests.
         * Note that dcpc_actv_reqs[] should always reflect which requests
         * we want to be in the set that is to be created. It is the
         * responsibility of the caller of dcpc_create_set() to adjust that
         * array accordingly beforehand.
         */
        for (i = 0; i < cpc_ncounters; i++) {
                if (dcpc_actv_reqs[i] != NULL)
                        active_requests++;
        }

        set = kmem_zalloc(sizeof (kcpc_set_t), KM_SLEEP);

        set->ks_req =
            kmem_zalloc(sizeof (kcpc_request_t) * active_requests, KM_SLEEP);

        set->ks_data =
            kmem_zalloc(active_requests * sizeof (uint64_t), KM_SLEEP);

        /*
         * Look for valid entries in the active requests array and populate
         * the request set for any entries found.
         */
        for (i = 0; i < cpc_ncounters; i++) {
                if (dcpc_actv_reqs[i] != NULL) {
                        dcpc_populate_set(c, dcpc_actv_reqs[i], set, reqno);
                        reqno++;
                }
        }

        return (set);
}

static int
dcpc_program_cpu_event(cpu_t *c)
{
        int i, j, subcode;
        kcpc_ctx_t *ctx, *octx;
        kcpc_set_t *set;

        set = dcpc_create_set(c);

        set->ks_ctx = ctx = kcpc_ctx_alloc(KM_SLEEP);
        ctx->kc_set = set;
        ctx->kc_cpuid = c->cpu_id;

        if (kcpc_assign_reqs(set, ctx) != 0)
                goto err;

        if (kcpc_configure_reqs(ctx, set, &subcode) != 0)
                goto err;

        for (i = 0; i < set->ks_nreqs; i++) {
                for (j = 0; j < cpc_ncounters; j++) {
                        if (dcpc_actv_reqs[j] != NULL &&
                            strcmp(set->ks_req[i].kr_event,
                            dcpc_actv_reqs[j]->dcpc_event_name) == 0) {
                                dcpc_actv_reqs[j]->dcpc_picno =
                                    set->ks_req[i].kr_picnum;
                        }
                }
        }

        /*
         * If we already have an active enabling then save the current cpc
         * context away.
         */
        octx = c->cpu_cpc_ctx;

        kcpc_cpu_program(c, ctx);

        if (octx != NULL) {
                kcpc_set_t *oset = octx->kc_set;
                kmem_free(oset->ks_data, oset->ks_nreqs * sizeof (uint64_t));
                kcpc_free_configs(oset);
                kcpc_free_set(oset);
                kcpc_ctx_free(octx);
        }

        return (0);

err:
        /*
         * We failed to configure this request up so free things up and
         * get out.
         */
        kcpc_free_configs(set);
        kmem_free(set->ks_data, set->ks_nreqs * sizeof (uint64_t));
        kcpc_free_set(set);
        kcpc_ctx_free(ctx);

        return (-1);
}

static void
dcpc_disable_cpu(cpu_t *c)
{
        kcpc_ctx_t *ctx;
        kcpc_set_t *set;

        /*
         * Leave this CPU alone if it's already offline.
         */
        if (c->cpu_flags & CPU_OFFLINE)
                return;

        /*
         * Grab CPUs CPC context before kcpc_cpu_stop() stops counters and
         * changes it.
         */
        ctx = c->cpu_cpc_ctx;

        kcpc_cpu_stop(c, B_FALSE);

        set = ctx->kc_set;

        kcpc_free_configs(set);
        kmem_free(set->ks_data, set->ks_nreqs * sizeof (uint64_t));
        kcpc_free_set(set);
        kcpc_ctx_free(ctx);
}

/*
 * The dcpc_*_interrupts() routines are responsible for manipulating the
 * per-CPU dcpc interrupt state byte. The purpose of the state byte is to
 * synchronize processing of hardware overflow interrupts wth configuration
 * changes made to the CPU performance counter subsystem by the dcpc provider.
 *
 * The dcpc provider claims ownership of the overflow interrupt mechanism
 * by transitioning the state byte from DCPC_INTR_INACTIVE (indicating the
 * dcpc provider is not in use) to DCPC_INTR_FREE (the dcpc provider owns the
 * overflow mechanism and interrupts may be processed). Before modifying
 * a CPUs configuration state the state byte is transitioned from
 * DCPC_INTR_FREE to DCPC_INTR_CONFIG ("configuration in process" state).
 * The hardware overflow handler, kcpc_hw_overflow_intr(), will only process
 * an interrupt when a configuration is not in process (i.e. the state is
 * marked as free). During interrupt processing the state is set to
 * DCPC_INTR_PROCESSING by the overflow handler. When the last dcpc based
 * enabling is removed, the state byte is set to DCPC_INTR_INACTIVE to indicate
 * the dcpc provider is no longer interested in overflow interrupts.
 */
static void
dcpc_block_interrupts(void)
{
        cpu_t *c = cpu_list;
        uint8_t *state;

        ASSERT(cpu_core[c->cpu_id].cpuc_dcpc_intr_state != DCPC_INTR_INACTIVE);

        do {
                state = &cpu_core[c->cpu_id].cpuc_dcpc_intr_state;

                while (atomic_cas_8(state, DCPC_INTR_FREE,
                    DCPC_INTR_CONFIG) != DCPC_INTR_FREE)
                        continue;

        } while ((c = c->cpu_next) != cpu_list);
}

/*
 * Set all CPUs dcpc interrupt state to DCPC_INTR_FREE to indicate that
 * overflow interrupts can be processed safely.
 */
static void
dcpc_release_interrupts(void)
{
        cpu_t *c = cpu_list;

        ASSERT(cpu_core[c->cpu_id].cpuc_dcpc_intr_state != DCPC_INTR_INACTIVE);

        do {
                cpu_core[c->cpu_id].cpuc_dcpc_intr_state = DCPC_INTR_FREE;
                membar_producer();
        } while ((c = c->cpu_next) != cpu_list);
}

/*
 * Transition all CPUs dcpc interrupt state from DCPC_INTR_INACTIVE to
 * to DCPC_INTR_FREE. This indicates that the dcpc provider is now
 * responsible for handling all overflow interrupt activity. Should only be
 * called before enabling the first dcpc based probe.
 */
static void
dcpc_claim_interrupts(void)
{
        cpu_t *c = cpu_list;

        ASSERT(cpu_core[c->cpu_id].cpuc_dcpc_intr_state == DCPC_INTR_INACTIVE);

        do {
                cpu_core[c->cpu_id].cpuc_dcpc_intr_state = DCPC_INTR_FREE;
                membar_producer();
        } while ((c = c->cpu_next) != cpu_list);
}

/*
 * Set all CPUs dcpc interrupt state to DCPC_INTR_INACTIVE to indicate that
 * the dcpc provider is no longer processing overflow interrupts. Only called
 * during removal of the last dcpc based enabling.
 */
static void
dcpc_surrender_interrupts(void)
{
        cpu_t *c = cpu_list;

        ASSERT(cpu_core[c->cpu_id].cpuc_dcpc_intr_state != DCPC_INTR_INACTIVE);

        do {
                cpu_core[c->cpu_id].cpuc_dcpc_intr_state = DCPC_INTR_INACTIVE;
                membar_producer();
        } while ((c = c->cpu_next) != cpu_list);
}

/*
 * dcpc_program_event() can be called owing to a new enabling or if a multi
 * overflow platform has disabled a request but needs to  program the requests
 * that are still valid.
 *
 * Every invocation of dcpc_program_event() will create a new kcpc_ctx_t
 * and a new request set which contains the new enabling and any old enablings
 * which are still valid (possible with multi-overflow platforms).
 */
static int
dcpc_program_event(dcpc_probe_t *pp)
{
        cpu_t *c;
        int ret = 0;

        ASSERT(MUTEX_HELD(&cpu_lock));

        kpreempt_disable();

        dcpc_block_interrupts();

        c = cpu_list;

        do {
                /*
                 * Skip CPUs that are currently offline.
                 */
                if (c->cpu_flags & CPU_OFFLINE)
                        continue;

                /*
                 * Stop counters but preserve existing DTrace CPC context
                 * if there is one.
                 *
                 * If we come here when the first event is programmed for a CPU,
                 * there should be no DTrace CPC context installed. In this
                 * case, kcpc_cpu_stop() will ensure that there is no other
                 * context on the CPU.
                 *
                 * If we add new enabling to the original one, the CPU should
                 * have the old DTrace CPC context which we need to keep around
                 * since dcpc_program_event() will add to it.
                 */
                if (c->cpu_cpc_ctx != NULL)
                        kcpc_cpu_stop(c, B_TRUE);
        } while ((c = c->cpu_next) != cpu_list);

        dcpc_release_interrupts();

        /*
         * If this enabling is being removed (in the case of a multi event
         * capable system with more than one active enabling), we can now
         * update the active request array to reflect the enablings that need
         * to be reprogrammed.
         */
        if (pp->dcpc_disabling == 1)
                dcpc_actv_reqs[pp->dcpc_actv_req_idx] = NULL;

        do {
                /*
                 * Skip CPUs that are currently offline.
                 */
                if (c->cpu_flags & CPU_OFFLINE)
                        continue;

                ret = dcpc_program_cpu_event(c);
        } while ((c = c->cpu_next) != cpu_list && ret == 0);

        /*
         * If dcpc_program_cpu_event() fails then it is because we couldn't
         * configure the requests in the set for the CPU and not because of
         * an error programming the hardware. If we have a failure here then
         * we assume no CPUs have been programmed in the above step as they
         * are all configured identically.
         */
        if (ret != 0) {
                pp->dcpc_enabled = 0;
                kpreempt_enable();
                return (-1);
        }

        if (pp->dcpc_disabling != 1)
                pp->dcpc_enabled = 1;

        kpreempt_enable();

        return (0);
}

/*ARGSUSED*/
static int
dcpc_enable(void *arg, dtrace_id_t id, void *parg)
{
        dcpc_probe_t *pp = parg;
        int i, found = 0;
        cpu_t *c;

        ASSERT(MUTEX_HELD(&cpu_lock));

        /*
         * Bail out if the counters are being used by a libcpc consumer.
         */
        rw_enter(&kcpc_cpuctx_lock, RW_READER);
        if (kcpc_cpuctx > 0) {
                rw_exit(&kcpc_cpuctx_lock);
                return (-1);
        }

        dtrace_cpc_in_use++;
        rw_exit(&kcpc_cpuctx_lock);

        /*
         * Locate this enabling in the first free entry of the active
         * request array.
         */
        for (i = 0; i < cpc_ncounters; i++) {
                if (dcpc_actv_reqs[i] == NULL) {
                        dcpc_actv_reqs[i] = pp;
                        pp->dcpc_actv_req_idx = i;
                        found = 1;
                        break;
                }
        }

        /*
         * If we couldn't find a slot for this probe then there is no
         * room at the inn.
         */
        if (!found) {
                dtrace_cpc_in_use--;
                return (-1);
        }

        ASSERT(pp->dcpc_actv_req_idx >= 0);

        /*
         * DTrace is taking over CPC contexts, so stop collecting
         * capacity/utilization data for all CPUs.
         */
        if (dtrace_cpc_in_use == 1)
                cu_disable();

        /*
         * The following must hold true if we are to (attempt to) enable
         * this request:
         *
         * 1) No enablings currently exist. We allow all platforms to
         * proceed if this is true.
         *
         * OR
         *
         * 2) If the platform is multi overflow capable and there are
         * less valid enablings than there are counters. There is no
         * guarantee that a platform can accommodate as many events as
         * it has counters for but we will at least try to program
         * up to that many requests.
         *
         * The 'dcpc_enablings' variable is implictly protected by locking
         * provided by the DTrace framework and the cpu management framework.
         */
        if (dcpc_enablings == 0 || (dcpc_mult_ovf_cap &&
            dcpc_enablings < cpc_ncounters)) {
                /*
                 * Before attempting to program the first enabling we need to
                 * invalidate any lwp-based contexts and lay claim to the
                 * overflow interrupt mechanism.
                 */
                if (dcpc_enablings == 0) {
                        kcpc_invalidate_all();
                        dcpc_claim_interrupts();
                }

                if (dcpc_program_event(pp) == 0) {
                        dcpc_enablings++;
                        return (0);
                }
        }

        /*
         * If active enablings existed before we failed to enable this probe
         * on a multi event capable platform then we need to restart counters
         * as they will have been stopped in the attempted configuration. The
         * context should now just contain the request prior to this failed
         * enabling.
         */
        if (dcpc_enablings > 0 && dcpc_mult_ovf_cap) {
                c = cpu_list;

                ASSERT(dcpc_mult_ovf_cap == 1);
                do {
                        /*
                         * Skip CPUs that are currently offline.
                         */
                        if (c->cpu_flags & CPU_OFFLINE)
                                continue;

                        kcpc_cpu_program(c, c->cpu_cpc_ctx);
                } while ((c = c->cpu_next) != cpu_list);
        }

        /*
         * Give up any claim to the overflow interrupt mechanism if no
         * dcpc based enablings exist.
         */
        if (dcpc_enablings == 0)
                dcpc_surrender_interrupts();

        dtrace_cpc_in_use--;
        dcpc_actv_reqs[pp->dcpc_actv_req_idx] = NULL;
        pp->dcpc_actv_req_idx = pp->dcpc_picno = -1;

        /*
         * If all probes are removed, enable capacity/utilization data
         * collection for every CPU.
         */
        if (dtrace_cpc_in_use == 0)
                cu_enable();

        return (-1);
}

/*
 * If only one enabling is active then remove the context and free
 * everything up. If there are multiple enablings active then remove this
 * one, its associated meta-data and re-program the hardware.
 */
/*ARGSUSED*/
static void
dcpc_disable(void *arg, dtrace_id_t id, void *parg)
{
        cpu_t *c;
        dcpc_probe_t *pp = parg;

        ASSERT(MUTEX_HELD(&cpu_lock));

        kpreempt_disable();

        /*
         * This probe didn't actually make it as far as being fully enabled
         * so we needn't do anything with it.
         */
        if (pp->dcpc_enabled == 0) {
                /*
                 * If we actually allocated this request a slot in the
                 * request array but failed to enabled it then remove the
                 * entry in the array.
                 */
                if (pp->dcpc_actv_req_idx >= 0) {
                        dcpc_actv_reqs[pp->dcpc_actv_req_idx] = NULL;
                        pp->dcpc_actv_req_idx = pp->dcpc_picno =
                            pp->dcpc_disabling = -1;
                }

                kpreempt_enable();
                return;
        }

        /*
         * If this is the only enabling then stop all the counters and
         * free up the meta-data.
         */
        if (dcpc_enablings == 1) {
                ASSERT(dtrace_cpc_in_use == 1);

                dcpc_block_interrupts();

                c = cpu_list;

                do {
                        dcpc_disable_cpu(c);
                } while ((c = c->cpu_next) != cpu_list);

                dcpc_actv_reqs[pp->dcpc_actv_req_idx] = NULL;
                dcpc_surrender_interrupts();
        } else {
                /*
                 * This platform can support multiple overflow events and
                 * the enabling being disabled is not the last one. Remove this
                 * enabling and re-program the hardware with the new config.
                 */
                ASSERT(dcpc_mult_ovf_cap);
                ASSERT(dcpc_enablings > 1);

                pp->dcpc_disabling = 1;
                (void) dcpc_program_event(pp);
        }

        kpreempt_enable();

        dcpc_enablings--;
        dtrace_cpc_in_use--;
        pp->dcpc_enabled = 0;
        pp->dcpc_actv_req_idx = pp->dcpc_picno = pp->dcpc_disabling = -1;

        /*
         * If all probes are removed, enable capacity/utilization data
         * collection for every CPU
         */
        if (dtrace_cpc_in_use == 0)
                cu_enable();
}

/*ARGSUSED*/
static int
dcpc_cpu_setup(cpu_setup_t what, processorid_t cpu, void *arg)
{
        cpu_t *c;
        uint8_t *state;

        ASSERT(MUTEX_HELD(&cpu_lock));

        switch (what) {
        case CPU_OFF:
                /*
                 * Offline CPUs are not allowed to take part so remove this
                 * CPU if we are actively tracing.
                 */
                if (dtrace_cpc_in_use) {
                        c = cpu_get(cpu);
                        state = &cpu_core[c->cpu_id].cpuc_dcpc_intr_state;

                        /*
                         * Indicate that a configuration is in process in
                         * order to stop overflow interrupts being processed
                         * on this CPU while we disable it.
                         */
                        while (atomic_cas_8(state, DCPC_INTR_FREE,
                            DCPC_INTR_CONFIG) != DCPC_INTR_FREE)
                                continue;

                        dcpc_disable_cpu(c);

                        /*
                         * Reset this CPUs interrupt state as the configuration
                         * has ended.
                         */
                        cpu_core[c->cpu_id].cpuc_dcpc_intr_state =
                            DCPC_INTR_FREE;
                        membar_producer();
                }
                break;

        case CPU_ON:
        case CPU_SETUP:
                /*
                 * This CPU is being initialized or brought online so program
                 * it with the current request set if we are actively tracing.
                 */
                if (dtrace_cpc_in_use) {
                        c = cpu_get(cpu);
                        (void) dcpc_program_cpu_event(c);
                }
                break;

        default:
                break;
        }

        return (0);
}

static dtrace_pattr_t dcpc_attr = {
{ DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_COMMON },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
{ DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_CPU },
{ DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_COMMON },
};

static dtrace_pops_t dcpc_pops = {
    dcpc_provide,
    NULL,
    dcpc_enable,
    dcpc_disable,
    NULL,
    NULL,
    NULL,
    NULL,
    dcpc_usermode,
    dcpc_destroy
};

/*ARGSUSED*/
static int
dcpc_open(dev_t *devp, int flag, int otyp, cred_t *cred_p)
{
        return (0);
}

/*ARGSUSED*/
static int
dcpc_info(dev_info_t *dip, ddi_info_cmd_t infocmd, void *arg, void **result)
{
        int error;

        switch (infocmd) {
        case DDI_INFO_DEVT2DEVINFO:
                *result = (void *)dcpc_devi;
                error = DDI_SUCCESS;
                break;
        case DDI_INFO_DEVT2INSTANCE:
                *result = (void *)0;
                error = DDI_SUCCESS;
                break;
        default:
                error = DDI_FAILURE;
        }
        return (error);
}

static int
dcpc_detach(dev_info_t *devi, ddi_detach_cmd_t cmd)
{
        switch (cmd) {
        case DDI_DETACH:
                break;
        case DDI_SUSPEND:
                return (DDI_SUCCESS);
        default:
                return (DDI_FAILURE);
        }

        if (dtrace_unregister(dcpc_pid) != 0)
                return (DDI_FAILURE);

        ddi_remove_minor_node(devi, NULL);

        mutex_enter(&cpu_lock);
        unregister_cpu_setup_func(dcpc_cpu_setup, NULL);
        mutex_exit(&cpu_lock);

        kmem_free(dcpc_actv_reqs, cpc_ncounters * sizeof (dcpc_probe_t *));

        kcpc_unregister_dcpc();

        return (DDI_SUCCESS);
}

static int
dcpc_attach(dev_info_t *devi, ddi_attach_cmd_t cmd)
{
        uint_t caps;
        char *attrs;

        switch (cmd) {
        case DDI_ATTACH:
                break;
        case DDI_RESUME:
                return (DDI_SUCCESS);
        default:
                return (DDI_FAILURE);
        }

        if (kcpc_pcbe_loaded() == -1)
                return (DDI_FAILURE);

        caps = kcpc_pcbe_capabilities();

        if (!(caps & CPC_CAP_OVERFLOW_INTERRUPT)) {
                cmn_err(CE_NOTE, "!dcpc: Counter Overflow not supported"\
                    " on this processor");
                return (DDI_FAILURE);
        }

        if (ddi_create_minor_node(devi, "dcpc", S_IFCHR, 0,
            DDI_PSEUDO, NULL) == DDI_FAILURE ||
            dtrace_register("cpc", &dcpc_attr, DTRACE_PRIV_KERNEL,
            NULL, &dcpc_pops, NULL, &dcpc_pid) != 0) {
                ddi_remove_minor_node(devi, NULL);
                return (DDI_FAILURE);
        }

        mutex_enter(&cpu_lock);
        register_cpu_setup_func(dcpc_cpu_setup, NULL);
        mutex_exit(&cpu_lock);

        dcpc_ovf_mask = (1 << cpc_ncounters) - 1;
        ASSERT(dcpc_ovf_mask != 0);

        if (caps & CPC_CAP_OVERFLOW_PRECISE)
                dcpc_mult_ovf_cap = 1;

        /*
         * Determine which, if any, mask attribute the back-end can use.
         */
        attrs = kcpc_list_attrs();
        if (strstr(attrs, "umask") != NULL)
                dcpc_mask_type |= DCPC_UMASK;
        else if (strstr(attrs, "emask") != NULL)
                dcpc_mask_type |= DCPC_EMASK;

        /*
         * The dcpc_actv_reqs array is used to store the requests that
         * we currently have programmed. The order of requests in this
         * array is not necessarily the order that the event appears in
         * the kcpc_request_t array. Once entered into a slot in the array
         * the entry is not moved until it's removed.
         */
        dcpc_actv_reqs =
            kmem_zalloc(cpc_ncounters * sizeof (dcpc_probe_t *), KM_SLEEP);

        dcpc_min_overflow = ddi_prop_get_int(DDI_DEV_T_ANY, devi,
            DDI_PROP_DONTPASS, "dcpc-min-overflow", DCPC_MIN_OVF_DEFAULT);

        kcpc_register_dcpc(dcpc_fire);

        ddi_report_dev(devi);
        dcpc_devi = devi;

        return (DDI_SUCCESS);
}

static struct cb_ops dcpc_cb_ops = {
        dcpc_open,              /* open */
        nodev,                  /* close */
        nulldev,                /* strategy */
        nulldev,                /* print */
        nodev,                  /* dump */
        nodev,                  /* read */
        nodev,                  /* write */
        nodev,                  /* ioctl */
        nodev,                  /* devmap */
        nodev,                  /* mmap */
        nodev,                  /* segmap */
        nochpoll,               /* poll */
        ddi_prop_op,            /* cb_prop_op */
        0,                      /* streamtab  */
        D_NEW | D_MP            /* Driver compatibility flag */
};

static struct dev_ops dcpc_ops = {
        DEVO_REV,               /* devo_rev, */
        0,                      /* refcnt  */
        dcpc_info,              /* get_dev_info */
        nulldev,                /* identify */
        nulldev,                /* probe */
        dcpc_attach,            /* attach */
        dcpc_detach,            /* detach */
        nodev,                  /* reset */
        &dcpc_cb_ops,           /* driver operations */
        NULL,                   /* bus operations */
        nodev,                  /* dev power */
        ddi_quiesce_not_needed  /* quiesce */
};

/*
 * Module linkage information for the kernel.
 */
static struct modldrv modldrv = {
        &mod_driverops,         /* module type */
        "DTrace CPC Module",    /* name of module */
        &dcpc_ops,              /* driver ops */
};

static struct modlinkage modlinkage = {
        MODREV_1,
        (void *)&modldrv,
        NULL
};

int
_init(void)
{
        return (mod_install(&modlinkage));
}

int
_info(struct modinfo *modinfop)
{
        return (mod_info(&modlinkage, modinfop));
}

int
_fini(void)
{
        return (mod_remove(&modlinkage));
}