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 2636238333F; Sun, 13 Sep 2026 03:27:19 +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=1789270041; cv=none; b=PxYzjnE9S5gjKZ36YBeK1FoXqN05nt69m2OVp1AwG4W5Kiese3SZOOuRWHEC/gE2lWa9+xfMD2bTq8VJi/8G8C2xI+WSYTKzOGN81yFeT/ka+ypkks+Fwkf1omll6hS8gz6vDidIDF91ZHa82ERBBTxxRkxSrvabGl2RuVZWZxc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789270041; c=relaxed/simple; bh=apH6VZyAnmLAyezMqL9Ah7ks15w3tPV5R2LG2bJnac0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tgKkrgPRK1oCQ4uqwRMqUfyZTLlRoSQ+eJOSApv2RR0+0GEeJRrnLpMAV3T5V4+dyIEtS97jv9rI8Gh57OG3+4RElbVB20grQ/pSkceunAqs1+yJLFDvOobPTqnr1wbjS907a2goXKVRd6rGvbkvVen9fq91lJBz7Wj2oN2wrLY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=K1gXYsPP; 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="K1gXYsPP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C85F1F000FF; Sun, 13 Sep 2026 03:27:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789270039; bh=TqR2Opoff9JKJPpDA+/gIuMlr5T0eNpJWAK21U2cxek=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=K1gXYsPPUkIF52bm65CNMDA7iIV4hvpxjMEKYiHgEMjRjt9YKKmCU7akLv2SG6goL OeET67aRh3UZ/DvCN3rIc405TqOreB6cpOr5yuaoVLzm4BooMqGBAgoDmateU0uwIW nKwncE56EM1dxxnBZMx1dApy3krYGHE004c7e5OU3nKWjVX5ZJbD3fSSxoapOOoXx9 74wff8xJNWN6M9G1kq7XQBzwLgsFB/dtxeaXee4Bz0XQdg1JSvUUeLXMRn7gp+tlAP LlummIDo+YpCWRJtfGB/hqY7GXjaMhZ3gF+Tm2CeungcgJC/9DcHl35Hc4UkHF/yhc L7T61kyH2wWZA== From: Arnaldo Carvalho de Melo To: Namhyung Kim 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: [PATCH v2 8/8] perf mem record: Request PERF_SAMPLE_CPU by default Date: Sun, 13 Sep 2026 00:26:28 -0300 Message-ID: <20260913032632.116277-9-acme@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260913032632.116277-1-acme@kernel.org> References: <20260913032632.116277-1-acme@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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). Assisted-by: LLM Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/Documentation/perf-mem.txt | 4 ++++ tools/perf/builtin-mem.c | 9 +++++++++ 2 files changed, 13 insertions(+) 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. "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..a708e2549bae4ce7 100644 --- a/tools/perf/builtin-mem.c +++ b/tools/perf/builtin-mem.c @@ -135,6 +135,15 @@ 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