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SubjectRe: [PATCH 2/3] perf tools: Fix SMT not detected with large core count
Em Tue, Nov 23, 2021 at 02:48:20PM -0800, Ian Rogers escreveu:
> sysfs__read_int returns 0 on success, and so the fast read path was
> always failing.

Please split this into two patches, the above part should be in one, and
the strtoull in another.

Also can't we just do as ./tools/perf/util/cputopo.c and use instead
core_cpus_list?

On a 5950x:

⬢[acme@toolbox perf]$ cat /sys/devices/system/cpu/cpu31/topology/core_cpus
80008000
⬢[acme@toolbox perf]$ cat /sys/devices/system/cpu/cpu31/topology/core_cpus_list
15,31
⬢[acme@toolbox perf]$ cat /sys/devices/system/cpu/cpu0/topology/core_cpus
00010001
⬢[acme@toolbox perf]$ cat /sys/devices/system/cpu/cpu0/topology/core_cpus_list
0,16
⬢[acme@toolbox perf]$

- Arnaldo

> 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.
>
> Fixes: bb629484d924 (perf tools: Simplify checking if SMT is active.)
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/util/smt.c | 68 ++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 58 insertions(+), 10 deletions(-)
>
> diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
> index 20bacd5972ad..2636be65305a 100644
> --- a/tools/perf/util/smt.c
> +++ b/tools/perf/util/smt.c
> @@ -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;
> - }
> + cached = true;
> return cached_result;
> }
> --
> 2.34.0.rc2.393.gf8c9666880-goog

--

- Arnaldo

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