From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 1EDAD2F12C5; Tue, 18 Nov 2025 06:50:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763448623; cv=none; b=fWkWO5VHN7cexJNMA6sNt+2gsnPpkTRZsJxIPzzfaeKyMxK+JgY1rcRPfQAnDJXzCdQwjJJemi4YP6vt7uuYRQKefL8PA0eI78+WGOTIL8pQ7+kwnreoCZLaA+f673AQsKEoJiU/6Ez4XKuIvbnQEJASL/S6QgRl5HidslAyTkM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763448623; c=relaxed/simple; bh=4YAcPvN5qtxecpZh9fXUCDPoMyUxrfJ0Xdtikv3lwpE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=e4tXDQPUw6FnGop2PG3sFuWac4HzZY8OmnXLI/VPjH2lQwOxMQ2CbTXbffhvIS59BtSmNquE+pBfAHU8TPtyxE53jces10/cEzZJCpVpZbAazKGlSPD+CwO7ldlaaLTA4+iYu8b9K6Tf1mUUNOxqdkojGNtLiCwEHfwBBnTZ6Yc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rXPproFn; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rXPproFn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3024CC4CEF1; Tue, 18 Nov 2025 06:50:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763448621; bh=4YAcPvN5qtxecpZh9fXUCDPoMyUxrfJ0Xdtikv3lwpE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rXPproFn9wD3gF/Xo1VaasNNW1A1NW4Xi0G79IFCs2h5QV8OgidYFJtZZDYZhdgba /Hz8rBnfSsz2TNwSfvK2rPQGwT0XCE4vkykh9YbMt0Q9PbCNxxUuWMlVUbLTjD1pzg nfYgvRScz95mGWatPUbHmjYMEEFom1ypOKpDg7WaoWem0Kjsz8bbLcUzTlzPaEMlYL NP57Q2gpav0V6G+Jvu8NuzPQY2DQp8uYgoIthuDdn5xYml8AdSX1/Jar1cPO91PNlO 8raSQxoox9l9fbUlyM1cXmTX/+7Vh0G4iRnV+j/HzNd/wlMKIY2QImYeZ+PhXc2a0C 3o8nGN+aXXKzw== Date: Mon, 17 Nov 2025 22:50:18 -0800 From: Namhyung Kim To: Ian Rogers Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Adrian Hunter , "Dr. David Alan Gilbert" , Yang Li , James Clark , Thomas Falcon , Thomas Richter , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Andi Kleen , Dapeng Mi Subject: Re: [PATCH v4 10/10] perf stat: Add no-affinity flag Message-ID: References: <20251113180517.44096-1-irogers@google.com> <20251113180517.44096-11-irogers@google.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Nov 17, 2025 at 08:32:20PM -0800, Ian Rogers wrote: > On Mon, Nov 17, 2025 at 6:41 PM Namhyung Kim wrote: > > > > On Thu, Nov 13, 2025 at 10:05:16AM -0800, Ian Rogers wrote: > > > Add flag that disables affinity behavior. Using sched_setaffinity to > > > place a perf thread on a CPU can avoid certain interprocessor > > > interrupts but may introduce a delay due to the scheduling, > > > particularly on loaded machines. Add a command line option to disable > > > the behavior. This behavior is less present in other tools like `perf > > > record`, as it uses a ring buffer and doesn't make repeated system > > > calls. > > > > > > Signed-off-by: Ian Rogers > > > --- > > > tools/perf/Documentation/perf-stat.txt | 4 ++++ > > > tools/perf/builtin-stat.c | 6 ++++++ > > > tools/perf/util/evlist.c | 2 +- > > > tools/perf/util/evlist.h | 1 + > > > 4 files changed, 12 insertions(+), 1 deletion(-) > > > > > > diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt > > > index 1a766d4a2233..1ffb510606af 100644 > > > --- a/tools/perf/Documentation/perf-stat.txt > > > +++ b/tools/perf/Documentation/perf-stat.txt > > > @@ -382,6 +382,10 @@ color the metric's computed value. > > > Don't print output, warnings or messages. This is useful with perf stat > > > record below to only write data to the perf.data file. > > > > > > +--no-affinity:: > > > +Don't change scheduler affinities when iterating over CPUs. Disables > > > +an optimization aimed at minimizing interprocessor interrupts. > > > + > > > STAT RECORD > > > ----------- > > > Stores stat data into perf data file. > > > diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c > > > index aec93b91fd11..fa42b08bd1df 100644 > > > --- a/tools/perf/builtin-stat.c > > > +++ b/tools/perf/builtin-stat.c > > > @@ -2415,6 +2415,7 @@ static int parse_tpebs_mode(const struct option *opt, const char *str, > > > int cmd_stat(int argc, const char **argv) > > > { > > > struct opt_aggr_mode opt_mode = {}; > > > + bool no_affinity = false; > > > struct option stat_options[] = { > > > OPT_BOOLEAN('T', "transaction", &transaction_run, > > > "hardware transaction statistics"), > > > @@ -2543,6 +2544,8 @@ int cmd_stat(int argc, const char **argv) > > > "don't print 'summary' for CSV summary output"), > > > OPT_BOOLEAN(0, "quiet", &quiet, > > > "don't print any output, messages or warnings (useful with record)"), > > > + OPT_BOOLEAN(0, "no-affinity", &no_affinity, > > > + "don't allow affinity optimizations aimed at reducing IPIs"), > > > > I know you want to add an option to disable the behaivor, but I think > > it'd better to have a positive option like just '--affinity'. Then we > > will have '--no-affinity' for free. :) The current form will allow > > '--no-no-affinity'. > > > > Then the variable also can be 'enable_affinity' or so. > > > > You can mention --no-affinity in the help message and the man page > > document so that users can discover the intention. > > I was trying to keep the code the same as the flag. I don't want to > have an affinity flag you need to set to true in say evlist, as that > will need updating in all users of the evlist or become a behavioral > change. We can have the evlist with no_affinity and invert the flag, > it just looks awkward imo. You can make the default to true and just update the users that want different behaviors. Thanks, Namhyung