perf_helpers.h

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/*****************************************************************/
/********* Begin perf_event low-level code ***********************/
/*****************************************************************/

/* In case headers aren't new enough to have __NR_perf_event_open */
#ifndef __NR_perf_event_open

#ifdef __powerpc__
#define __NR_perf_event_open    319
#elif defined(__x86_64__)
#define __NR_perf_event_open    298
#elif defined(__i386__)
#define __NR_perf_event_open    336
#elif defined(__arm__)
#define __NR_perf_event_open    364
#endif

#endif

static long
sys_perf_event_open( struct perf_event_attr *hw_event,
        pid_t pid, int cpu, int group_fd, unsigned long flags )
{
    int ret;

    ret = syscall( __NR_perf_event_open,
            hw_event, pid, cpu, group_fd, flags );

    return ret;
}

#if defined(__x86_64__) || defined(__i386__)


static inline unsigned long long rdtsc(void) {

    unsigned a,d;

    __asm__ volatile("rdtsc" : "=a" (a), "=d" (d));

    return ((unsigned long long)a) | (((unsigned long long)d) << 32);
}

static inline unsigned long long rdpmc(unsigned int counter) {

    unsigned int low, high;

    __asm__ volatile("rdpmc" : "=a" (low), "=d" (high) : "c" (counter));

    return (unsigned long long)low | ((unsigned long long)high) <<32;
}

#define barrier() __asm__ volatile("" ::: "memory")

/* based on the code in include/uapi/linux/perf_event.h */
static inline unsigned long long mmap_read_self(void *addr,
                     unsigned long long *en,
                     unsigned long long *ru) {

    struct perf_event_mmap_page *pc = addr;

    uint32_t seq, time_mult, time_shift, index, width;
    int64_t count;
    uint64_t enabled, running;
    uint64_t cyc, time_offset;
    int64_t pmc = 0;
    uint64_t quot, rem;
    uint64_t delta = 0;


    do {
        /* The kernel increments pc->lock any time */
        /* perf_event_update_userpage() is called */
        /* So by checking now, and the end, we */
        /* can see if an update happened while we */
        /* were trying to read things, and re-try */
        /* if something changed */
        /* The barrier ensures we get the most up to date */
        /* version of the pc->lock variable */

        seq=pc->lock;
        barrier();

        /* For multiplexing */
        /* time_enabled is time the event was enabled */
        enabled = pc->time_enabled;
        /* time_running is time the event was actually running */
        running = pc->time_running;

        /* if cap_user_time is set, we can use rdtsc */
        /* to calculate more exact enabled/running time */
        /* for more accurate multiplex calculations */
        if ( (pc->cap_user_time) && (enabled != running)) {
            cyc = rdtsc();
            time_offset = pc->time_offset;
            time_mult = pc->time_mult;
            time_shift = pc->time_shift;

            quot=(cyc>>time_shift);
            rem = cyc & (((uint64_t)1 << time_shift) - 1);
            delta = time_offset + (quot * time_mult) +
                ((rem * time_mult) >> time_shift);
        }
        enabled+=delta;

        /* actually do the measurement */

        /* Index of register to read */
        /* 0 means stopped/not-active */
        /* Need to subtract 1 to get actual index to rdpmc() */
        index = pc->index;

        /* count is the value of the counter the last time */
        /* the kernel read it */
        /* If we don't sign extend it, we get large negative */
        /* numbers which break if an IOC_RESET is done */
        width = pc->pmc_width;
        count = pc->offset;
        count<<=(64-width);
        count>>=(64-width);

        /* Ugh, libpfm4 perf_event.h has cap_usr_rdpmc */
        /* while actual perf_event.h has cap_user_rdpmc */

        /* Only read if rdpmc enabled and event index valid */
        /* Otherwise return the older (out of date?) count value */
        if (pc->cap_usr_rdpmc && index) {

            /* Read counter value */
            pmc = rdpmc(index-1);

            /* sign extend result */
            pmc<<=(64-width);
            pmc>>=(64-width);

            /* add current count into the existing kernel count */
            count+=pmc;

            /* Only adjust if index is valid */
            running+=delta;
        } else {
            /* Falling back because rdpmc not supported */
            /* for this event.              */
            return 0xffffffffffffffffULL;
        }

        barrier();

    } while (pc->lock != seq);

    if (en) *en=enabled;
    if (ru) *ru=running;

    return count;
}

#else
static inline unsigned long long mmap_read_self(void *addr,
                     unsigned long long *en,
                     unsigned long long *ru) {

    (void)addr;

    *en=0;
    *ru=0;

    return (unsigned long long)(-1);
}

#endif

/* These functions are based on builtin-record.c in the  */
/* kernel's tools/perf directory.                        */
/* This code is from a really ancient version of perf */
/* And should be updated/commented properly */


static uint64_t
mmap_read_head( pe_event_info_t *pe )
{
    struct perf_event_mmap_page *pc = pe->mmap_buf;
    int head;

    if ( pc == NULL ) {
        PAPIERROR( "perf_event_mmap_page is NULL" );
        return 0;
    }

    head = pc->data_head;
    rmb();

    return head;
}

static void
mmap_write_tail( pe_event_info_t *pe, uint64_t tail )
{
    struct perf_event_mmap_page *pc = pe->mmap_buf;

    /* ensure all reads are done before we write the tail out. */
    pc->data_tail = tail;
}

/* Does the kernel define these somewhere? */
struct ip_event {
    struct perf_event_header header;
    uint64_t ip;
};
struct lost_event {
    struct perf_event_header header;
    uint64_t id;
    uint64_t lost;
};
typedef union event_union {
    struct perf_event_header header;
    struct ip_event ip;
    struct lost_event lost;
} perf_sample_event_t;

/* Should re-write with comments if we ever figure out what's */
/* going on here.                                             */
static void
mmap_read( int cidx, ThreadInfo_t **thr, pe_event_info_t *pe,
           int profile_index )
{
    uint64_t head = mmap_read_head( pe );
    uint64_t old = pe->tail;
    unsigned char *data = ((unsigned char*)pe->mmap_buf) + getpagesize();
    int diff;

    diff = head - old;
    if ( diff < 0 ) {
        SUBDBG( "WARNING: failed to keep up with mmap data. head = %" PRIu64
            ",  tail = %" PRIu64 ". Discarding samples.\n", head, old );
        /* head points to a known good entry, start there. */
        old = head;
    }

    for( ; old != head; ) {
        perf_sample_event_t *event = ( perf_sample_event_t * )& data[old & pe->mask];
        perf_sample_event_t event_copy;
        size_t size = event->header.size;

        /* Event straddles the mmap boundary -- header should always */
        /* be inside due to u64 alignment of output.                 */
        if ( ( old & pe->mask ) + size != ( ( old + size ) & pe->mask ) ) {
            uint64_t offset = old;
            uint64_t len = min( sizeof ( *event ), size ), cpy;
            void *dst = &event_copy;

            do {
                cpy = min( pe->mask + 1 - ( offset & pe->mask ), len );
                memcpy( dst, &data[offset & pe->mask], cpy );
                offset += cpy;
                dst = ((unsigned char*)dst) + cpy;
                len -= cpy;
            } while ( len );

            event = &event_copy;
        }
        old += size;

        SUBDBG( "event->type = %08x\n", event->header.type );
        SUBDBG( "event->size = %d\n", event->header.size );

        switch ( event->header.type ) {
            case PERF_RECORD_SAMPLE:
                _papi_hwi_dispatch_profile( ( *thr )->running_eventset[cidx],
                    ( caddr_t ) ( unsigned long ) event->ip.ip,
                    0, profile_index );
                break;

            case PERF_RECORD_LOST:
                SUBDBG( "Warning: because of a mmap buffer overrun, %" PRId64
                    " events were lost.\n"
                    "Loss was recorded when counter id %#"PRIx64
                    " overflowed.\n", event->lost.lost, event->lost.id );
                break;
            default:
                SUBDBG( "Error: unexpected header type - %d\n",
                    event->header.type );
                break;
        }
    }

    pe->tail = old;
    mmap_write_tail( pe, old );
}