linux/tools/perf/arch/x86/util/tsc.c

#include <stdbool.h>
#include <errno.h>

#include <linux/perf_event.h>

#include "../../perf.h"
#include "../../util/types.h"
#include "../../util/debug.h"
#include "tsc.h"

u64 perf_time_to_tsc(u64 ns, struct perf_tsc_conversion *tc)
{
	u64 t, quot, rem;

	t = ns - tc->time_zero;
	quot = t / tc->time_mult;
	rem  = t % tc->time_mult;
	return (quot << tc->time_shift) +
	       (rem << tc->time_shift) / tc->time_mult;
}

u64 tsc_to_perf_time(u64 cyc, struct perf_tsc_conversion *tc)
{
	u64 quot, rem;

	quot = cyc >> tc->time_shift;
	rem  = cyc & ((1 << tc->time_shift) - 1);
	return tc->time_zero + quot * tc->time_mult +
	       ((rem * tc->time_mult) >> tc->time_shift);
}

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;
}