Commit 1276ade6 authored by Ian Rogers's avatar Ian Rogers Committed by Arnaldo Carvalho de Melo
Browse files

perf tsc: Add cpuinfo fall back for arch_get_tsc_freq() 



The CPUID method of arch_get_tsc_freq fails for older Intel processors,
such as Skylake. Compute using /proc/cpuinfo.

Reviewed-by: default avatarKan Liang <kan.liang@linux.intel.com>
Signed-off-by: default avatarIan Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Caleb Biggers <caleb.biggers@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.garry@huawei.com>
Cc: Kshipra Bopardikar <kshipra.bopardikar@intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Perry Taylor <perry.taylor@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20220718164312.3994191-3-irogers@google.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent bc2373a5

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

+48 −4
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#include <linux/types.h>

#include <math.h>

#include <string.h>



#include "../../../util/debug.h"

#include "../../../util/tsc.h"

#include "cpuid.h"
@@ -14,6 +16,44 @@ u64 rdtsc(void) 
	return low | ((u64)high) << 32;

}



/*

 * Derive the TSC frequency in Hz from the /proc/cpuinfo, for example:

 * ...

 * model name      : Intel(R) Xeon(R) Gold 6154 CPU @ 3.00GHz

 * ...

 * will return 3000000000.

 */

static double cpuinfo_tsc_freq(void)

{

	double result = 0;

	FILE *cpuinfo;

	char *line = NULL;

	size_t len = 0;



	cpuinfo = fopen("/proc/cpuinfo", "r");

	if (!cpuinfo) {

		pr_err("Failed to read /proc/cpuinfo for TSC frequency");

		return NAN;

	}

	while (getline(&line, &len, cpuinfo) > 0) {

		if (!strncmp(line, "model name", 10)) {

			char *pos = strstr(line + 11, " @ ");



			if (pos && sscanf(pos, " @ %lfGHz", &result) == 1) {

				result *= 1000000000;

				goto out;

			}

		}

	}

out:

	if (fpclassify(result) == FP_ZERO)

		pr_err("Failed to find TSC frequency in /proc/cpuinfo");



	free(line);

	fclose(cpuinfo);

	return result;

}



double arch_get_tsc_freq(void)

{

	unsigned int a, b, c, d, lvl;
@@ -33,13 +73,17 @@ double arch_get_tsc_freq(void) 
	 * Don't support Time Stamp Counter and

	 * Nominal Core Crystal Clock Information Leaf.

	 */

	if (lvl < 0x15)

		return 0;

	if (lvl < 0x15) {

		tsc = cpuinfo_tsc_freq();

		return tsc;

	}



	cpuid(0x15, 0, &a, &b, &c, &d);

	/* TSC frequency is not enumerated */

	if (!a || !b || !c)

		return 0;

	if (!a || !b || !c) {

		tsc = cpuinfo_tsc_freq();

		return tsc;

	}



	tsc = (double)c * (double)b / (double)a;

	return tsc;