i86pc/os/intr.c

	intr.c revision c81508f4cade391b84f6d917b985789f5c899222
/*
 * 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 2006 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

#include <sys/cpuvar.h>
#include <sys/regset.h>
#include <sys/psw.h>
#include <sys/types.h>
#include <sys/thread.h>
#include <sys/systm.h>
#include <sys/segments.h>
#include <sys/pcb.h>
#include <sys/trap.h>
#include <sys/ftrace.h>
#include <sys/traptrace.h>
#include <sys/clock.h>
#include <sys/panic.h>
#include <sys/disp.h>
#include <vm/seg_kp.h>
#include <sys/stack.h>
#include <sys/sysmacros.h>
#include <sys/cmn_err.h>
#include <sys/kstat.h>
#include <sys/smp_impldefs.h>
#include <sys/pool_pset.h>
#include <sys/zone.h>
#include <sys/bitmap.h>

#if defined(__amd64)

#if defined(__lint)
/*
 * atomic_btr32() is a gcc __inline__ function, defined in <asm/bitmap.h>
 * For lint purposes, define it here.
 */
uint_t
atomic_btr32(uint32_t *pending, uint_t pil)
{
    return (*pending &= ~(1 << pil));
}
#else

extern uint_t atomic_btr32(uint32_t *pending, uint_t pil);

#endif

/*
 * This code is amd64-only for now, but as time permits, we should
 * use this on i386 too.
 */

/*
 * Some questions to ponder:
 * -    in several of these routines, we make multiple calls to tsc_read()
 *  without invoking functions .. couldn't we just reuse the same
 *  timestamp sometimes?
 * -    if we have the inline, we can probably make set_base_spl be a
 *  C routine too.
 */

static uint_t
bsrw_insn(uint16_t mask)
{
    uint_t index = sizeof (mask) * NBBY - 1;

    ASSERT(mask != 0);

    while ((mask & (1 << index)) == 0)
        index--;
    return (index);
}

/*
 * Do all the work necessary to set up the cpu and thread structures
 * to dispatch a high-level interrupt.
 *
 * Returns 0 if we're -not- already on the high-level interrupt stack,
 * (and *must* switch to it), non-zero if we are already on that stack.
 *
 * Called with interrupts masked.
 * The 'pil' is already set to the appropriate level for rp->r_trapno.
 */
int
hilevel_intr_prolog(struct cpu *cpu, uint_t pil, uint_t oldpil, struct regs *rp)
{
    struct machcpu *mcpu = &cpu->cpu_m;
    uint_t mask;
    hrtime_t intrtime;

    ASSERT(pil > LOCK_LEVEL);

    if (pil == CBE_HIGH_PIL) {
        cpu->cpu_profile_pil = oldpil;
        if (USERMODE(rp->r_cs)) {
            cpu->cpu_profile_pc = 0;
            cpu->cpu_profile_upc = rp->r_pc;
        } else {
            cpu->cpu_profile_pc = rp->r_pc;
            cpu->cpu_profile_upc = 0;
        }
    }

    mask = cpu->cpu_intr_actv & CPU_INTR_ACTV_HIGH_LEVEL_MASK;
    if (mask != 0) {
        int nestpil;

        /*
         * We have interrupted another high-level interrupt.
         * Load starting timestamp, compute interval, update
         * cumulative counter.
         */
        nestpil = bsrw_insn((uint16_t)mask);
        ASSERT(nestpil < pil);
        intrtime = tsc_read() -
            mcpu->pil_high_start[nestpil - (LOCK_LEVEL + 1)];
        mcpu->intrstat[nestpil][0] += intrtime;
        cpu->cpu_intracct[cpu->cpu_mstate] += intrtime;
        /*
         * Another high-level interrupt is active below this one, so
         * there is no need to check for an interrupt thread.  That
         * will be done by the lowest priority high-level interrupt
         * active.
         */
    } else {
        kthread_t *t = cpu->cpu_thread;

        /*
         * See if we are interrupting a low-level interrupt thread.
         * If so, account for its time slice only if its time stamp
         * is non-zero.
         */
        if ((t->t_flag & T_INTR_THREAD) != 0 && t->t_intr_start != 0) {
            intrtime = tsc_read() - t->t_intr_start;
            mcpu->intrstat[t->t_pil][0] += intrtime;
            cpu->cpu_intracct[cpu->cpu_mstate] += intrtime;
            t->t_intr_start = 0;
        }
    }

    /*
     * Store starting timestamp in CPU structure for this PIL.
     */
    mcpu->pil_high_start[pil - (LOCK_LEVEL + 1)] = tsc_read();

    ASSERT((cpu->cpu_intr_actv & (1 << pil)) == 0);

    if (pil == 15) {
        /*
         * To support reentrant level 15 interrupts, we maintain a
         * recursion count in the top half of cpu_intr_actv.  Only
         * when this count hits zero do we clear the PIL 15 bit from
         * the lower half of cpu_intr_actv.
         */
        uint16_t *refcntp = (uint16_t *)&cpu->cpu_intr_actv + 1;
        (*refcntp)++;
    }

    mask = cpu->cpu_intr_actv;

    cpu->cpu_intr_actv |= (1 << pil);

    return (mask & CPU_INTR_ACTV_HIGH_LEVEL_MASK);
}

/*
 * Does most of the work of returning from a high level interrupt.
 *
 * Returns 0 if there are no more high level interrupts (in which
 * case we must switch back to the interrupted thread stack) or
 * non-zero if there are more (in which case we should stay on it).
 *
 * Called with interrupts masked
 */
int
hilevel_intr_epilog(struct cpu *cpu, uint_t pil, uint_t oldpil, uint_t vecnum)
{
    struct machcpu *mcpu = &cpu->cpu_m;
    uint_t mask;
    hrtime_t intrtime;

    ASSERT(mcpu->mcpu_pri == pil);

    cpu->cpu_stats.sys.intr[pil - 1]++;

    ASSERT(cpu->cpu_intr_actv & (1 << pil));

    if (pil == 15) {
        /*
         * To support reentrant level 15 interrupts, we maintain a
         * recursion count in the top half of cpu_intr_actv.  Only
         * when this count hits zero do we clear the PIL 15 bit from
         * the lower half of cpu_intr_actv.
         */
        uint16_t *refcntp = (uint16_t *)&cpu->cpu_intr_actv + 1;

        ASSERT(*refcntp > 0);

        if (--(*refcntp) == 0)
            cpu->cpu_intr_actv &= ~(1 << pil);
    } else {
        cpu->cpu_intr_actv &= ~(1 << pil);
    }

    ASSERT(mcpu->pil_high_start[pil - (LOCK_LEVEL + 1)] != 0);

    intrtime = tsc_read() - mcpu->pil_high_start[pil - (LOCK_LEVEL + 1)];
    mcpu->intrstat[pil][0] += intrtime;
    cpu->cpu_intracct[cpu->cpu_mstate] += intrtime;

    /*
     * Check for lower-pil nested high-level interrupt beneath
     * current one.  If so, place a starting timestamp in its
     * pil_high_start entry.
     */
    mask = cpu->cpu_intr_actv & CPU_INTR_ACTV_HIGH_LEVEL_MASK;
    if (mask != 0) {
        int nestpil;

        /*
         * find PIL of nested interrupt
         */
        nestpil = bsrw_insn((uint16_t)mask);
        ASSERT(nestpil < pil);
        mcpu->pil_high_start[nestpil - (LOCK_LEVEL + 1)] = tsc_read();
        /*
         * (Another high-level interrupt is active below this one,
         * so there is no need to check for an interrupt
         * thread.  That will be done by the lowest priority
         * high-level interrupt active.)
         */
    } else {
        /*
         * Check to see if there is a low-level interrupt active.
         * If so, place a starting timestamp in the thread
         * structure.
         */
        kthread_t *t = cpu->cpu_thread;

        if (t->t_flag & T_INTR_THREAD)
            t->t_intr_start = tsc_read();
    }

    mcpu->mcpu_pri = oldpil;
    (void) (*setlvlx)(oldpil, vecnum);

    return (cpu->cpu_intr_actv & CPU_INTR_ACTV_HIGH_LEVEL_MASK);
}

/*
 * Set up the cpu, thread and interrupt thread structures for
 * executing an interrupt thread.  The new stack pointer of the
 * interrupt thread (which *must* be switched to) is returned.
 */
caddr_t
intr_thread_prolog(struct cpu *cpu, caddr_t stackptr, uint_t pil)
{
    struct machcpu *mcpu = &cpu->cpu_m;
    kthread_t *t, *volatile it;

    ASSERT(pil > 0);
    ASSERT((cpu->cpu_intr_actv & (1 << pil)) == 0);
    cpu->cpu_intr_actv |= (1 << pil);

    /*
     * Get set to run an interrupt thread.
     * There should always be an interrupt thread, since we
     * allocate one for each level on each CPU.
     *
     * t_intr_start could be zero due to cpu_intr_swtch_enter.
     */
    t = cpu->cpu_thread;
    if ((t->t_flag & T_INTR_THREAD) && t->t_intr_start != 0) {
        hrtime_t intrtime = tsc_read() - t->t_intr_start;
        mcpu->intrstat[t->t_pil][0] += intrtime;
        cpu->cpu_intracct[cpu->cpu_mstate] += intrtime;
        t->t_intr_start = 0;
    }

    ASSERT(SA((uintptr_t)stackptr) == (uintptr_t)stackptr);

    t->t_sp = (uintptr_t)stackptr;  /* mark stack in curthread for resume */

    /*
     * unlink the interrupt thread off the cpu
     *
     * Note that the code in kcpc_overflow_intr -relies- on the
     * ordering of events here - in particular that t->t_lwp of
     * the interrupt thread is set to the pinned thread *before*
     * curthread is changed.
     */
    it = cpu->cpu_intr_thread;
    cpu->cpu_intr_thread = it->t_link;
    it->t_intr = t;
    it->t_lwp = t->t_lwp;

    /*
     * (threads on the interrupt thread free list could have state
     * preset to TS_ONPROC, but it helps in debugging if
     * they're TS_FREE.)
     */
    it->t_state = TS_ONPROC;

    cpu->cpu_thread = it;       /* new curthread on this cpu */
    it->t_pil = (uchar_t)pil;
    it->t_pri = intr_pri + (pri_t)pil;
    it->t_intr_start = tsc_read();

    return (it->t_stk);
}


#ifdef DEBUG
int intr_thread_cnt;
#endif

/*
 * Called with interrupts disabled
 */
void
intr_thread_epilog(struct cpu *cpu, uint_t vec, uint_t oldpil)
{
    struct machcpu *mcpu = &cpu->cpu_m;
    kthread_t *t;
    kthread_t *it = cpu->cpu_thread;    /* curthread */
    uint_t pil, basespl;
    hrtime_t intrtime;

    pil = it->t_pil;
    cpu->cpu_stats.sys.intr[pil - 1]++;

    ASSERT(it->t_intr_start != 0);
    intrtime = tsc_read() - it->t_intr_start;
    mcpu->intrstat[pil][0] += intrtime;
    cpu->cpu_intracct[cpu->cpu_mstate] += intrtime;

    ASSERT(cpu->cpu_intr_actv & (1 << pil));
    cpu->cpu_intr_actv &= ~(1 << pil);

    /*
     * If there is still an interrupted thread underneath this one
     * then the interrupt was never blocked and the return is
     * fairly simple.  Otherwise it isn't.
     */
    if ((t = it->t_intr) == NULL) {
        /*
         * The interrupted thread is no longer pinned underneath
         * the interrupt thread.  This means the interrupt must
         * have blocked, and the interrupted thread has been
         * unpinned, and has probably been running around the
         * system for a while.
         *
         * Since there is no longer a thread under this one, put
         * this interrupt thread back on the CPU's free list and
         * resume the idle thread which will dispatch the next
         * thread to run.
         */
#ifdef DEBUG
        intr_thread_cnt++;
#endif
        cpu->cpu_stats.sys.intrblk++;
        /*
         * Set CPU's base SPL based on active interrupts bitmask
         */
        set_base_spl();
        basespl = cpu->cpu_base_spl;
        mcpu->mcpu_pri = basespl;
        (*setlvlx)(basespl, vec);
        (void) splhigh();
        it->t_state = TS_FREE;
        /*
         * Return interrupt thread to pool
         */
        it->t_link = cpu->cpu_intr_thread;
        cpu->cpu_intr_thread = it;
        swtch();
        /*NOTREACHED*/
    }

    /*
     * Return interrupt thread to the pool
     */
    it->t_link = cpu->cpu_intr_thread;
    cpu->cpu_intr_thread = it;
    it->t_state = TS_FREE;

    basespl = cpu->cpu_base_spl;
    pil = MAX(oldpil, basespl);
    mcpu->mcpu_pri = pil;
    (*setlvlx)(pil, vec);
    t->t_intr_start = tsc_read();
    cpu->cpu_thread = t;
}

/*
 * Called with interrupts disabled by an interrupt thread to determine
 * how much time has elapsed. See interrupt.s:intr_get_time() for detailed
 * theory of operation.
 */
uint64_t
intr_thread_get_time(struct cpu *cpu)
{
    struct machcpu *mcpu = &cpu->cpu_m;
    kthread_t *t = cpu->cpu_thread;
    uint64_t time, delta, ret;
    uint_t pil = t->t_pil;

    ASSERT((cpu->cpu_intr_actv & CPU_INTR_ACTV_HIGH_LEVEL_MASK) == 0);
    ASSERT(t->t_flag & T_INTR_THREAD);
    ASSERT(pil != 0);
    ASSERT(t->t_intr_start != 0);

    time = tsc_read();
    delta = time - t->t_intr_start;
    t->t_intr_start = time;

    time = mcpu->intrstat[pil][0] + delta;
    ret = time - mcpu->intrstat[pil][1];
    mcpu->intrstat[pil][0] = time;
    mcpu->intrstat[pil][1] = time;
    cpu->cpu_intracct[cpu->cpu_mstate] += delta;

    return (ret);
}

caddr_t
dosoftint_prolog(
    struct cpu *cpu,
    caddr_t stackptr,
    uint32_t st_pending,
    uint_t oldpil)
{
    kthread_t *t, *volatile it;
    struct machcpu *mcpu = &cpu->cpu_m;
    uint_t pil;

top:
    ASSERT(st_pending == mcpu->mcpu_softinfo.st_pending);

    pil = bsrw_insn((uint16_t)st_pending);
    if (pil <= oldpil || pil <= cpu->cpu_base_spl)
        return (0);

    /*
     * XX64 Sigh.
     *
     * This is a transliteration of the i386 assembler code for
     * soft interrupts.  One question is "why does this need
     * to be atomic?"  One possible race is -other- processors
     * posting soft interrupts to us in set_pending() i.e. the
     * CPU might get preempted just after the address computation,
     * but just before the atomic transaction, so another CPU would
     * actually set the original CPU's st_pending bit.  However,
     * it looks like it would be simpler to disable preemption there.
     * Are there other races for which preemption control doesn't work?
     *
     * The i386 assembler version -also- checks to see if the bit
     * being cleared was actually set; if it wasn't, it rechecks
     * for more.  This seems a bit strange, as the only code that
     * ever clears the bit is -this- code running with interrupts
     * disabled on -this- CPU.  This code would probably be cheaper:
     *
     * atomic_and_32((uint32_t *)&mcpu->mcpu_softinfo.st_pending,
     *   ~(1 << pil));
     *
     * and t->t_preempt--/++ around set_pending() even cheaper,
     * but at this point, correctness is critical, so we slavishly
     * emulate the i386 port.
     */
    if (atomic_btr32((uint32_t *)&mcpu->mcpu_softinfo.st_pending, pil)
        == 0) {
        st_pending = mcpu->mcpu_softinfo.st_pending;
        goto top;
    }

    mcpu->mcpu_pri = pil;
    (*setspl)(pil);

    /*
     * Get set to run interrupt thread.
     * There should always be an interrupt thread since we
     * allocate one for each level on the CPU.
     */
    it = cpu->cpu_intr_thread;
    cpu->cpu_intr_thread = it->t_link;

    /* t_intr_start could be zero due to cpu_intr_swtch_enter. */
    t = cpu->cpu_thread;
    if ((t->t_flag & T_INTR_THREAD) && t->t_intr_start != 0) {
        hrtime_t intrtime = tsc_read() - t->t_intr_start;
        mcpu->intrstat[pil][0] += intrtime;
        cpu->cpu_intracct[cpu->cpu_mstate] += intrtime;
        t->t_intr_start = 0;
    }

    /*
     * Note that the code in kcpc_overflow_intr -relies- on the
     * ordering of events here - in particular that t->t_lwp of
     * the interrupt thread is set to the pinned thread *before*
     * curthread is changed.
     */
    it->t_lwp = t->t_lwp;
    it->t_state = TS_ONPROC;

    /*
     * Push interrupted thread onto list from new thread.
     * Set the new thread as the current one.
     * Set interrupted thread's T_SP because if it is the idle thread,
     * resume() may use that stack between threads.
     */

    ASSERT(SA((uintptr_t)stackptr) == (uintptr_t)stackptr);
    t->t_sp = (uintptr_t)stackptr;

    it->t_intr = t;
    cpu->cpu_thread = it;

    /*
     * Set bit for this pil in CPU's interrupt active bitmask.
     */
    ASSERT((cpu->cpu_intr_actv & (1 << pil)) == 0);
    cpu->cpu_intr_actv |= (1 << pil);

    /*
     * Initialize thread priority level from intr_pri
     */
    it->t_pil = (uchar_t)pil;
    it->t_pri = (pri_t)pil + intr_pri;
    it->t_intr_start = tsc_read();

    return (it->t_stk);
}

void
dosoftint_epilog(struct cpu *cpu, uint_t oldpil)
{
    struct machcpu *mcpu = &cpu->cpu_m;
    kthread_t *t, *it;
    uint_t pil, basespl;
    hrtime_t intrtime;

    it = cpu->cpu_thread;
    pil = it->t_pil;

    cpu->cpu_stats.sys.intr[pil - 1]++;

    ASSERT(cpu->cpu_intr_actv & (1 << pil));
    cpu->cpu_intr_actv &= ~(1 << pil);
    intrtime = tsc_read() - it->t_intr_start;
    mcpu->intrstat[pil][0] += intrtime;
    cpu->cpu_intracct[cpu->cpu_mstate] += intrtime;

    /*
     * If there is still an interrupted thread underneath this one
     * then the interrupt was never blocked and the return is
     * fairly simple.  Otherwise it isn't.
     */
    if ((t = it->t_intr) == NULL) {
        /*
         * Put thread back on the interrupt thread list.
         * This was an interrupt thread, so set CPU's base SPL.
         */
        set_base_spl();
        it->t_state = TS_FREE;
        it->t_link = cpu->cpu_intr_thread;
        cpu->cpu_intr_thread = it;
        (void) splhigh();
        swtch();
        /*NOTREACHED*/
    }
    it->t_link = cpu->cpu_intr_thread;
    cpu->cpu_intr_thread = it;
    it->t_state = TS_FREE;
    cpu->cpu_thread = t;
    if (t->t_flag & T_INTR_THREAD)
        t->t_intr_start = tsc_read();
    basespl = cpu->cpu_base_spl;
    pil = MAX(oldpil, basespl);
    mcpu->mcpu_pri = pil;
    (*setspl)(pil);
}

/*
 * Make the interrupted thread 'to' be runnable.
 *
 * Since t->t_sp has already been saved, t->t_pc is all
 * that needs to be set in this function.
 *
 * Returns the interrupt level of the interrupt thread.
 */
int
intr_passivate(
    kthread_t *it,      /* interrupt thread */
    kthread_t *t)       /* interrupted thread */
{
    extern void _sys_rtt();

    ASSERT(it->t_flag & T_INTR_THREAD);
    ASSERT(SA(t->t_sp) == t->t_sp);

    t->t_pc = (uintptr_t)_sys_rtt;
    return (it->t_pil);
}

#endif  /* __amd64 */

/*
 * Create interrupt kstats for this CPU.
 */
void
cpu_create_intrstat(cpu_t *cp)
{
    int     i;
    kstat_t     *intr_ksp;
    kstat_named_t   *knp;
    char        name[KSTAT_STRLEN];
    zoneid_t    zoneid;

    ASSERT(MUTEX_HELD(&cpu_lock));

    if (pool_pset_enabled())
        zoneid = GLOBAL_ZONEID;
    else
        zoneid = ALL_ZONES;

    intr_ksp = kstat_create_zone("cpu", cp->cpu_id, "intrstat", "misc",
        KSTAT_TYPE_NAMED, PIL_MAX * 2, NULL, zoneid);

    /*
     * Initialize each PIL's named kstat
     */
    if (intr_ksp != NULL) {
        intr_ksp->ks_update = cpu_kstat_intrstat_update;
        knp = (kstat_named_t *)intr_ksp->ks_data;
        intr_ksp->ks_private = cp;
        for (i = 0; i < PIL_MAX; i++) {
            (void) snprintf(name, KSTAT_STRLEN, "level-%d-time",
                i + 1);
            kstat_named_init(&knp[i * 2], name, KSTAT_DATA_UINT64);
            (void) snprintf(name, KSTAT_STRLEN, "level-%d-count",
                i + 1);
            kstat_named_init(&knp[(i * 2) + 1], name,
                KSTAT_DATA_UINT64);
        }
        kstat_install(intr_ksp);
    }
}

/*
 * Delete interrupt kstats for this CPU.
 */
void
cpu_delete_intrstat(cpu_t *cp)
{
    kstat_delete_byname_zone("cpu", cp->cpu_id, "intrstat", ALL_ZONES);
}

/*
 * Convert interrupt statistics from CPU ticks to nanoseconds and
 * update kstat.
 */
int
cpu_kstat_intrstat_update(kstat_t *ksp, int rw)
{
    kstat_named_t   *knp = ksp->ks_data;
    cpu_t       *cpup = (cpu_t *)ksp->ks_private;
    int     i;
    hrtime_t    hrt;

    if (rw == KSTAT_WRITE)
        return (EACCES);

    for (i = 0; i < PIL_MAX; i++) {
        hrt = (hrtime_t)cpup->cpu_m.intrstat[i + 1][0];
        tsc_scalehrtime(&hrt);
        knp[i * 2].value.ui64 = (uint64_t)hrt;
        knp[(i * 2) + 1].value.ui64 = cpup->cpu_stats.sys.intr[i];
    }

    return (0);
}

/*
 * An interrupt thread is ending a time slice, so compute the interval it
 * ran for and update the statistic for its PIL.
 */
void
cpu_intr_swtch_enter(kthread_id_t t)
{
    uint64_t    interval;
    uint64_t    start;
    cpu_t       *cpu;

    ASSERT((t->t_flag & T_INTR_THREAD) != 0);
    ASSERT(t->t_pil > 0 && t->t_pil <= LOCK_LEVEL);

    /*
     * We could be here with a zero timestamp. This could happen if:
     * an interrupt thread which no longer has a pinned thread underneath
     * it (i.e. it blocked at some point in its past) has finished running
     * its handler. intr_thread() updated the interrupt statistic for its
     * PIL and zeroed its timestamp. Since there was no pinned thread to
     * return to, swtch() gets called and we end up here.
     *
     * Note that we use atomic ops below (cas64 and atomic_add_64), which
     * we don't use in the functions above, because we're not called
     * with interrupts blocked, but the epilog/prolog functions are.
     */
    if (t->t_intr_start) {
        do {
            start = t->t_intr_start;
            interval = tsc_read() - start;
        } while (cas64(&t->t_intr_start, start, 0) != start);
        cpu = CPU;
        cpu->cpu_m.intrstat[t->t_pil][0] += interval;

        atomic_add_64((uint64_t *)&cpu->cpu_intracct[cpu->cpu_mstate],
            interval);
    } else
        ASSERT(t->t_intr == NULL);
}

/*
 * An interrupt thread is returning from swtch(). Place a starting timestamp
 * in its thread structure.
 */
void
cpu_intr_swtch_exit(kthread_id_t t)
{
    uint64_t ts;

    ASSERT((t->t_flag & T_INTR_THREAD) != 0);
    ASSERT(t->t_pil > 0 && t->t_pil <= LOCK_LEVEL);

    do {
        ts = t->t_intr_start;
    } while (cas64(&t->t_intr_start, ts, tsc_read()) != ts);
}