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 046912D7DEA; Thu, 6 Nov 2025 05:29:22 +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=1762406964; cv=none; b=s+ovVBCcNhJtFiPu+SMRuqoofHosuvPOtN3tHqLD36Pu6v56wo2kgTtpwfiDCdPHt+zLNfzuGq57sY3Y9eqhiZmYechVozEv1Y65ZHEWnl/skYJxS0XDE9sWJIcVCXLJly0xDcMbkMl10fYOcTEJna1fK/kZfIJWSMiyUfBF9Ls= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762406964; c=relaxed/simple; bh=SkogPYk4QLHERBeaT4qVGwEzmHQkhK1nc4xnVl1EdPk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hVjAS+SGeBamu39Wgtn/V7vYegGihcXPoN68lbq9qfn38KpOW0JBiofCmgTR0W9gLh6k+PBR29IIbtUxpfIshS6vrzorZzsnMAEoNX5E5pYIRrZASkUjXnj+tMZSqDEKMdAjdAz407HdjTGELFPAdEtJTNPgibec/3z57+UNtYw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bHegBrAd; 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="bHegBrAd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8E49C116C6; Thu, 6 Nov 2025 05:29:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762406962; bh=SkogPYk4QLHERBeaT4qVGwEzmHQkhK1nc4xnVl1EdPk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bHegBrAdfErawxZXx4M7QRv7Aze//66m+TtohMSriyskyC1dnpbcNpYLrL4JGhz1x PLO8bf2s8xuQYBY+my7UlNpFRyvmdf5v7strNJTT6Io0g+4hCJRLnzHxs/DiS/rc41 IIxFNfxITJA/zowoFNzWBJGzEChKy0HlT5CaG2Iq7Mnbc1ksudm0mw4BafRSUK8QcK xl8wIoP0u5hgU9XgzURyFcTbvgs3UYoqZt7S6iFpwqPZhtc3f17+RmUJt5zwstFPNV W6GRingAz1iPABVW4jw/un+nx787xlj4YyfUpxDA0GIRXxi+lhJNWHUJFltIKfyE06 JlRGBpMCdinPA== Date: Wed, 5 Nov 2025 21:29:20 -0800 From: Namhyung Kim To: Ian Rogers Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Adrian Hunter , James Clark , Xu Yang , Chun-Tse Shao , Thomas Richter , Sumanth Korikkar , Collin Funk , Thomas Falcon , Howard Chu , Dapeng Mi , Levi Yun , Yang Li , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org Subject: Re: [PATCH v1 00/22] Switch the default perf stat metrics to json Message-ID: References: <20251024175857.808401-1-irogers@google.com> 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 Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Nov 03, 2025 at 09:09:14PM -0800, Ian Rogers wrote: > On Mon, Nov 3, 2025 at 8:47 PM Namhyung Kim wrote: > > > > Hi Ian, > > > > On Fri, Oct 24, 2025 at 10:58:35AM -0700, Ian Rogers wrote: > > > Prior to this series stat-shadow would produce hard coded metrics if > > > certain events appeared in the evlist. This series produces equivalent > > > json metrics and cleans up the consequences in tests and display > > > output. A before and after of the default display output on a > > > tigerlake is: > > > > > > Before: > > > ``` > > > $ perf stat -a sleep 1 > > > > > > Performance counter stats for 'system wide': > > > > > > 16,041,816,418 cpu-clock # 15.995 CPUs utilized > > > 5,749 context-switches # 358.376 /sec > > > 121 cpu-migrations # 7.543 /sec > > > 1,806 page-faults # 112.581 /sec > > > 825,965,204 instructions # 0.70 insn per cycle > > > 1,180,799,101 cycles # 0.074 GHz > > > 168,945,109 branches # 10.532 M/sec > > > 4,629,567 branch-misses # 2.74% of all branches > > > # 30.2 % tma_backend_bound > > > # 7.8 % tma_bad_speculation > > > # 47.1 % tma_frontend_bound > > > # 14.9 % tma_retiring > > > ``` > > > > > > After: > > > ``` > > > $ perf stat -a sleep 1 > > > > > > Performance counter stats for 'system wide': > > > > > > 2,890 context-switches # 179.9 cs/sec cs_per_second > > > 16,061,923,339 cpu-clock # 16.0 CPUs CPUs_utilized > > > 43 cpu-migrations # 2.7 migrations/sec migrations_per_second > > > 5,645 page-faults # 351.5 faults/sec page_faults_per_second > > > 5,708,413 branch-misses # 1.4 % branch_miss_rate (88.83%) > > > 429,978,120 branches # 26.8 K/sec branch_frequency (88.85%) > > > 1,626,915,897 cpu-cycles # 0.1 GHz cycles_frequency (88.84%) > > > 2,556,805,534 instructions # 1.5 instructions insn_per_cycle (88.86%) > > > TopdownL1 # 20.1 % tma_backend_bound > > > # 40.5 % tma_bad_speculation (88.90%) > > > # 17.2 % tma_frontend_bound (78.05%) > > > # 22.2 % tma_retiring (88.89%) > > > > > > 1.002994394 seconds time elapsed > > > ``` > > > > While this looks nicer, I worry about the changes in the output. And I'm > > curious why only the "After" output shows the multiplexing percent. > > > > > > > > Having the metrics in json brings greater uniformity, allows events to > > > be shared by metrics, and it also allows descriptions like: > > > ``` > > > $ perf list cs_per_second > > > ... > > > cs_per_second > > > [Context switches per CPU second] > > > ``` > > > > > > A thorn in the side of doing this work was that the hard coded metrics > > > were used by perf script with '-F metric'. This functionality didn't > > > work for me (I was testing `perf record -e instructions,cycles` and > > > then `perf script -F metric` but saw nothing but empty lines) > > > > The documentation says: > > > > With the metric option perf script can compute metrics for > > sampling periods, similar to perf stat. This requires > > specifying a group with multiple events defining metrics with the :S option > > for perf record. perf will sample on the first event, and > > print computed metrics for all the events in the group. Please note > > that the metric computed is averaged over the whole sampling > > period (since the last sample), not just for the sample point. > > > > So I guess it should have 'S' modifiers in a group. > > Thanks Namhyung. Yes, this is the silly behavior where leader sample > events are both treated as an event but then the constituent parts > turned into individual events with the period set to the leader sample > read counts. Most recently this behavior was disabled by struct > perf_tool's dont_split_sample_group in the case of perf inject as it > causes events to be processed multiple times. The perf script behavior > doesn't rely anywhere on the grouping of the leader sample events and > even with it the metric format option doesn't work either - I'll save > pasting a screen full of blank lines here. Right, it seems to be broken at some point. > > > > but anyway I decided to fix it to the best of my ability in this > > > series. So the script side counters were removed and the regular ones > > > associated with the evsel used. The json metrics were all searched > > > looking for ones that have a subset of events matching those in the > > > perf script session, and all metrics are printed. This is kind of > > > weird as the counters are being set by the period of samples, but I > > > carried the behavior forward. I suspect there needs to be follow up > > > work to make this better, but what is in the series is superior to > > > what is currently in the tree. Follow up work could include finding > > > metrics for the machine in the perf.data rather than using the host, > > > allowing multiple metrics even if the metric ids of the events differ, > > > fixing pre-existing `perf stat record/report` issues, etc. > > > > > > There is a lot of stat tests that, for example, assume '-e > > > instructions,cycles' will produce an IPC metric. These things needed > > > tidying as now the metric must be explicitly asked for and when doing > > > this ones using software events were preferred to increase > > > compatibility. As the test updates were numerous they are distinct to > > > the patches updating the functionality causing periods in the series > > > where not all tests are passing. If this is undesirable the test fixes > > > can be squashed into the functionality updates. > > > > Hmm.. how many of them? I think it'd better to have the test changes at > > the same time so that we can assure test success count after the change. > > Can the test changes be squashed into one or two commits? > > So the patches are below. The first set are all clean up: > > > > Ian Rogers (22): > > > perf evsel: Remove unused metric_events variable > > > perf metricgroup: Update comment on location of metric_event list > > > perf metricgroup: Missed free on error path > > > perf metricgroup: When copy metrics copy default information > > > perf metricgroup: Add care to picking the evsel for displaying a > > > metric > > > perf jevents: Make all tables static I've applied most of this part to perf-tools-next, will take a look at others later. Thanks, Namhyung > > Then there is the addition of the legacy metrics as json: > > > > perf expr: Add #target_cpu literal > > > perf jevents: Add set of common metrics based on default ones > > > perf jevents: Add metric DefaultShowEvents > > > perf stat: Add detail -d,-dd,-ddd metrics > > Then there is the change to make perf script metric format work: > > > > perf script: Change metric format to use json metrics > > Then there is a clean up patch: > > > > perf stat: Remove hard coded shadow metrics > > Then there are fixes to perf stat's already broken output: > > > > perf stat: Fix default metricgroup display on hybrid > > > perf stat: Sort default events/metrics > > > perf stat: Remove "unit" workarounds for metric-only > > Then there are 7 patches updating test expectations. Each patch deals > with a separate test to make the resolution clear. > > > > perf test stat+json: Improve metric-only testing > > > perf test stat: Ignore failures in Default[234] metricgroups > > > perf test stat: Update std_output testing metric expectations > > > perf test metrics: Update all metrics for possibly failing default > > > metrics > > > perf test stat: Update shadow test to use metrics > > > perf test stat: Update test expectations and events > > > perf test stat csv: Update test expectations and events > > The patch "perf jevents: Add set of common metrics based on default > ones" most impacts the output but we don't want to verify the default > stat output with the hardcoded metrics that are removed in "perf stat: > Remove hard coded shadow metrics". Having a test for both hard coded > and json metrics in an intermediate state makes little sense and the > default output is impacting by the 3 patches fixing it and removing > workarounds. > > It is possible to squash things together but I think something is lost > in doing so, hence presenting it this way. > > Thanks, > Ian