From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B9BED4E1C6E; Wed, 16 Sep 2026 21:50:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789595445; cv=none; b=XyUvvDkSEMBHpPVySr2zM6EO51+QGId/3L/W3cWi6e71WxDRSs6FeG7Oagc4O9k5d2itbII/kYkSFwAA6xkCHxCigQyNgK9sw3ZCZV5bmIGDuZzJDSzAsdNL2Xd8YmQVX6wJNpVzJOY/ZL2FnhKLqhOjNfYrKfX5EkSCiQW5e7k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789595445; c=relaxed/simple; bh=abQippdCg51EPTGOaMBpu4rIEx5kWERpF412DcYUUHw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=nvVsQpvMxbjdv6pRXhaZgywWy8WZgi+t0KZ6gbuxeg7WXt8rqCpsaULCJbiN2H1MbqC5j+YB222kIq75lBnNi1E/P4xbyMNKCloZOZR0tf02p11pdjAVvP+v22RRype97V11Nxu+aUSvtMlMAB28oxfuneGWP1UEOvg6JaZYN4I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fzSyqKTS; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fzSyqKTS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A1B561F000FF; Wed, 16 Sep 2026 21:50:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789595434; bh=E5bM/grQTeAiimVn59VYKO/69gbhLhhyXSv4xi05fbQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=fzSyqKTS5j/hWKqFuRyuXfWPiQWT/IkAc0GJiZvPf1rtfJHnrSEJGA6zU6kftNZ7k jlcOgt37Pf4Tv917Qi6zBqkWvfGCwPs58KGsQR46BcKo+U1RoiUibKYq1XngO/kmv/ 4NGhre96vBSa69TOKE/bJ6DKRCMX/ogiufi1L3XHLn0/n2yXnhgwxXpSb5w8QQCvlq iscbUFJJZTTp1kxJM/hsdezfH5INTO+pnjKE293uPVOjv6mZCgZHG1SvxnQiVstd1T 7NAYG158hASaTjMr4i10H0zvkhSsXHgQeWkucc7f4zngha6dELMXqhMlEUOx1dPM7J Mk+fcVE6KpJ1w== Date: Wed, 16 Sep 2026 14:50:32 -0700 From: Namhyung Kim To: Arnaldo Carvalho de Melo Cc: Ingo Molnar , Thomas Gleixner , James Clark , Jiri Olsa , Ian Rogers , Adrian Hunter , Clark Williams , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Arnaldo Carvalho de Melo Subject: Re: [PATCH 11/12] perf mem record: Request PERF_SAMPLE_CPU by default Message-ID: References: <20260916114740.48230-1-acme@kernel.org> <20260916114740.48230-12-acme@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260916114740.48230-12-acme@kernel.org> On Wed, Sep 16, 2026 at 08:47:38AM -0300, Arnaldo Carvalho de Melo wrote: > From: Arnaldo Carvalho de Melo > > The data-type profiling per-sample stream keys cross-CPU contention on > sample->cpu: without PERF_SAMPLE_CPU the cpu field is the (u32)-1 "no > CPU info" sentinel, documented as such in perf_session__deliver_event(), > and same-instance reads and writes from different cores are > indistinguishable from same-CPU traffic, so pahole's false-sharing > detector cannot tell them apart. > > builtin-record.c already defines --sample-cpu and 'perf mem record' > forwards unknown options to the record parser, so passing it explicitly > works today; make it the default, next to the -d (addr) and -W (weight) > the command already requests, documenting it in perf-mem(1). > > The rec_argv array is sized as nine arguments per memory PMU plus the > user arguments, not counting the arguments __cmd_record() adds itself, > up to eight with all the optional flags. On PMUs with separate load and > store events the four event arguments plus the fixed ones already filled > the array to its last slot, so this new argument would write past it; > reserve space for the fixed arguments explicitly. > > Assisted-by: LLM > Signed-off-by: Arnaldo Carvalho de Melo > --- > tools/perf/Documentation/perf-mem.txt | 4 ++++ > tools/perf/builtin-mem.c | 18 ++++++++++++++++-- > 2 files changed, 20 insertions(+), 2 deletions(-) > > diff --git a/tools/perf/Documentation/perf-mem.txt b/tools/perf/Documentation/perf-mem.txt > index 4d164836d0943119..fe51c5e3333dc4a0 100644 > --- a/tools/perf/Documentation/perf-mem.txt > +++ b/tools/perf/Documentation/perf-mem.txt > @@ -14,6 +14,10 @@ DESCRIPTION > ----------- > "perf mem record" runs a command and gathers memory operation data > from it, into perf.data. Perf record options are accepted and are passed through. > +It also requests the address (-d), the weight (-W, where supported) and the > +CPU id (--sample-cpu) of every sampled access by default; the CPU id is what > +lets per-sample analysis tell reads and writes to the same data from > +different cores apart from same-CPU traffic. I guess the data source of samples can tell that on supported platforms. Probably we can check TID for concurrent access, wdyt? Thanks, Namhyung > > "perf mem report" displays the result. It invokes perf report with the > right set of options to display a memory access profile. By default, loads > diff --git a/tools/perf/builtin-mem.c b/tools/perf/builtin-mem.c > index 6101a26b3a781e69..6f38cda1a45ada16 100644 > --- a/tools/perf/builtin-mem.c > +++ b/tools/perf/builtin-mem.c > @@ -99,8 +99,13 @@ static int __cmd_record(int argc, const char **argv, struct perf_mem *mem, > argc = parse_options(argc, argv, options, record_usage, > PARSE_OPT_KEEP_UNKNOWN); > > - /* Max number of arguments multiplied by number of PMUs that can support them. */ > - rec_argc = argc + 9 * (perf_pmu__mem_events_num_mem_pmus(pmu) + 1); > + /* > + * Max number of arguments multiplied by number of PMUs that can > + * support them, plus the arguments added directly below, at most: > + * "record", "-W", "-d", "--sample-cpu", "--phys-data", > + * "--data-page-size", "--all-user" and "--all-kernel". > + */ > + rec_argc = argc + 8 + 9 * (perf_pmu__mem_events_num_mem_pmus(pmu) + 1); > > if (mem->cpu_list) > rec_argc += 2; > @@ -135,6 +140,15 @@ static int __cmd_record(int argc, const char **argv, struct perf_mem *mem, > > rec_argv[i++] = "-d"; > > + /* > + * The data-type profiling per-sample stream keys cross-CPU > + * contention on sample->cpu (PERF_SAMPLE_CPU); without it the cpu > + * field is the (u32)-1 'no CPU info' sentinel and same-instance > + * reads and writes from different cores are indistinguishable > + * from same-CPU traffic. > + */ > + rec_argv[i++] = "--sample-cpu"; > + > if (mem->phys_addr) > rec_argv[i++] = "--phys-data"; > > -- > 2.55.0 >