linux-kernel - Re: [PATCH v2 3/3] perf tool: simplify checking active smt

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Message-ID: <20200429181609.GG30487@kernel.org>
Date:   Wed, 29 Apr 2020 15:16:09 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Andi Kleen <ak@...ux.intel.com>,
        Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
Subject: Re: [PATCH v2 3/3] perf tool: simplify checking active smt

Em Wed, Apr 29, 2020 at 07:23:41PM +0300, Konstantin Khlebnikov escreveu:
> SMT now could be disabled via "/sys/devices/system/cpu/smt/control".
> Status shown in "/sys/devices/system/cpu/smt/active" simply as "0" / "1".
> 
> If this knob isn't here then fallback to checking topology as before.

I've manually applied this one, thanks, please check my perf/core branch
later before resending 2/3, thanks.

- Arnaldo
 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> ---
>  tools/perf/util/smt.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
> index dc37b5abd1c3..c398528d1006 100644
> --- a/tools/perf/util/smt.c
> +++ b/tools/perf/util/smt.c
> @@ -19,6 +19,9 @@ int smt_on(void)
>  	if (cached)
>  		return cached_result;
>  
> +	if (sysfs__read_int("devices/system/cpu/smt/active", &active) > 0)
> +		goto done;
> +
>  	ncpu = sysconf(_SC_NPROCESSORS_CONF);
>  	for (cpu = 0; cpu < ncpu; cpu++) {
>  		char fn[256];
> @@ -37,6 +40,7 @@ int smt_on(void)
>  	active = str && (strchr(str, ',') != NULL || strchr(str, '-') != NULL);
>  	free(str);
>  
> +done:
>  	if (!cached) {
>  		cached_result = active;
>  		cached = true;
> 

-- 

- Arnaldo