linux-kernel - Re: [PATCH] perf arm64: Fix read PMU cpu slots

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Message-ID: <2e392aa9-859a-75ef-eb3e-1870b1e78061@linux.alibaba.com>
Date:   Mon, 24 Jul 2023 15:40:12 +0800
From:   Jing Zhang <renyu.zj@...ux.alibaba.com>
To:     Haixin Yu <yuhaixin.yhx@...ux.alibaba.com>,
        John Garry <john.g.garry@...cle.com>,
        Will Deacon <will@...nel.org>,
        James Clark <james.clark@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf arm64: Fix read PMU cpu slots



在 2023/7/24 下午1:06, Haixin Yu 写道:
> Commit f8ad6018ce3c ("perf pmu: Remove duplication around
>  EVENT_SOURCE_DEVICE_PATH") uses sysfs__read_ull to read a full
> sysfs path, which will never success. Fix it by read file directly.
> 
> Signed-off-by: Haixin Yu <yuhaixin.yhx@...ux.alibaba.com>
> ---
>  tools/perf/arch/arm64/util/pmu.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/arch/arm64/util/pmu.c b/tools/perf/arch/arm64/util/pmu.c
> index 561de0cb6b95..512a8f13c4de 100644
> --- a/tools/perf/arch/arm64/util/pmu.c
> +++ b/tools/perf/arch/arm64/util/pmu.c
> @@ -54,10 +54,11 @@ double perf_pmu__cpu_slots_per_cycle(void)
>  		perf_pmu__pathname_scnprintf(path, sizeof(path),
>  					     pmu->name, "caps/slots");
>  		/*
> -		 * The value of slots is not greater than 32 bits, but sysfs__read_int
> -		 * can't read value with 0x prefix, so use sysfs__read_ull instead.
> +		 * The value of slots is not greater than 32 bits, but
> +		 * filename__read_int can't read value with 0x prefix,
> +		 * so use filename__read_ull instead.
>  		 */
> -		sysfs__read_ull(path, &slots);
> +		filename__read_ull(path, &slots);
>  	}
>  
>  	return slots ? (double)slots : NAN;

Yes, the function perf_pmu__pathname_scnprintf returns the complete slots file path "/sys/bus/xxxxx/caps/slots",
and sysfs__read_ull will add the prefix "/sys" to the path, so the final file path becomes "/sys/sys/bus/xxxx/caps/slots"
which does not exist, and the slots file cannot be successfully read, so sysfs__read_ull needs to be changed to the
filename__read_ull.

I tested it and it works well.

Tested-by: Jing Zhang <renyu.zj@...ux.alibaba.com>