Commit 0ce05781 authored by Ian Rogers's avatar Ian Rogers Committed by Arnaldo Carvalho de Melo
Browse files

perf tools: Fix SMT fallback with large core counts 



strtoull can only read a 64-bit bitmap. On an AMD EPYC core_cpus may look
like:

00000000,00000000,00000000,00000001,00000000,00000000,00000000,00000001

and so the sibling wasn't spotted. Fix by writing a simple hweight string
parser.

Signed-off-by: default avatarIan Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20211124001231.3277836-3-irogers@google.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 6d18804b

tools/perf/util/smt.c

+58 −10
Original line number Diff line number Diff line
@@ -5,6 +5,56 @@ 
#include "api/fs/fs.h"

#include "smt.h"



/**

 * hweight_str - Returns the number of bits set in str. Stops at first non-hex

 *	       or ',' character.

 */

static int hweight_str(char *str)

{

	int result = 0;



	while (*str) {

		switch (*str++) {

		case '0':

		case ',':

			break;

		case '1':

		case '2':

		case '4':

		case '8':

			result++;

			break;

		case '3':

		case '5':

		case '6':

		case '9':

		case 'a':

		case 'A':

		case 'c':

		case 'C':

			result += 2;

			break;

		case '7':

		case 'b':

		case 'B':

		case 'd':

		case 'D':

		case 'e':

		case 'E':

			result += 3;

			break;

		case 'f':

		case 'F':

			result += 4;

			break;

		default:

			goto done;

		}

	}

done:

	return result;

}



int smt_on(void)

{

	static bool cached;
@@ -15,9 +65,12 @@ int smt_on(void) 
	if (cached)

		return cached_result;



	if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0)

		goto done;

	if (sysfs__read_int("devices/system/cpu/smt/active", &cached_result) >= 0) {

		cached = true;

		return cached_result;

	}



	cached_result = 0;

	ncpu = sysconf(_SC_NPROCESSORS_CONF);

	for (cpu = 0; cpu < ncpu; cpu++) {

		unsigned long long siblings;
@@ -35,18 +88,13 @@ int smt_on(void) 
				continue;

		}

		/* Entry is hex, but does not have 0x, so need custom parser */

		siblings = strtoull(str, NULL, 16);

		siblings = hweight_str(str);

		free(str);

		if (hweight64(siblings) > 1) {

		if (siblings > 1) {

			cached_result = 1;

			cached = true;

			break;

		}

	}

	if (!cached) {

		cached_result = 0;

done:

	cached = true;

	}

	return cached_result;

}