tsc.c

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// SPDX-License-Identifier: GPL-2.0
#include <stdbool.h>
#include <errno.h>

#include <linux/perf_event.h>

#include "../../perf.h"
#include <linux/types.h>
#include "../../util/debug.h"
#include "../../util/tsc.h"

int perf_read_tsc_conversion(const struct perf_event_mmap_page *pc,
                 struct perf_tsc_conversion *tc)
{
    bool cap_user_time_zero;
    u32 seq;
    int i = 0;

    while (1) {
        seq = pc->lock;
        rmb();
        tc->time_mult = pc->time_mult;
        tc->time_shift = pc->time_shift;
        tc->time_zero = pc->time_zero;
        cap_user_time_zero = pc->cap_user_time_zero;
        rmb();
        if (pc->lock == seq && !(seq & 1))
            break;
        if (++i > 10000) {
            pr_debug("failed to get perf_event_mmap_page lock\n");
            return -EINVAL;
        }
    }

    if (!cap_user_time_zero)
        return -EOPNOTSUPP;

    return 0;
}

u64 rdtsc(void)
{
    unsigned int low, high;

    asm volatile("rdtsc" : "=a" (low), "=d" (high));

    return low | ((u64)high) << 32;
}

int perf_event__synth_time_conv(const struct perf_event_mmap_page *pc,
                struct perf_tool *tool,
                perf_event__handler_t process,
                struct machine *machine)
{
    union perf_event event = {
        .time_conv = {
            .header = {
                .type = PERF_RECORD_TIME_CONV,
                .size = sizeof(struct time_conv_event),
            },
        },
    };
    struct perf_tsc_conversion tc;
    int err;

    if (!pc)
        return 0;
    err = perf_read_tsc_conversion(pc, &tc);
    if (err == -EOPNOTSUPP)
        return 0;
    if (err)
        return err;

    pr_debug2("Synthesizing TSC conversion information\n");

    event.time_conv.time_mult  = tc.time_mult;
    event.time_conv.time_shift = tc.time_shift;
    event.time_conv.time_zero  = tc.time_zero;

    return process(tool, &event, NULL, machine);
}