From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5EFD8C433F5 for ; Thu, 30 Sep 2021 22:58:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4AF0D61A50 for ; Thu, 30 Sep 2021 22:58:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235396AbhI3XAF (ORCPT ); Thu, 30 Sep 2021 19:00:05 -0400 Received: from mail-lf1-f46.google.com ([209.85.167.46]:40888 "EHLO mail-lf1-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348921AbhI3XAC (ORCPT ); Thu, 30 Sep 2021 19:00:02 -0400 Received: by mail-lf1-f46.google.com with SMTP id b15so31326655lfe.7; Thu, 30 Sep 2021 15:58:18 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=XyaNvh9Xs6AkDGl/pcn1sfY9JyqCtB/i0b3ibbUEjPU=; b=dWqMuUqkRrK6htRz3LMLeJzisXgwrZsCZuI7aS//dKPSNb9eFu4DVsqJr43k/XO3vG 6lhHTMzGMaz/7lrReHe4o3eT1nk1WaadvzcRhwCM1FArnv0/IvfOd+u8vzm8sPXpDxCW 2Wn66oXGiaFbZZiiElTmbzlg7T3VyTmKu2KAAESoWiBjo4tNIBhCHh3J59LNuTuZNYel IBMvm9nvEEXTjI/TmPNdWyUyJR2VJFKySIhcwhfE7BzLcxe91OetrEoLJNN8ye6BgzhE x5A3CF4ODdgkZw+jRea4dXLhMgujUyvf3ceB9cyNZCNHODvvkHCieD0HdBtZwFd5CLD1 gFxQ== X-Gm-Message-State: AOAM531czLgECHirXnN+SGI5xr+zcWz3XCbL7m4uZeWEiZoP4sGJF03+ E5Iqg1aizKAQG9JLMUFzj6PJr8+BtXnHFjkqGnU= X-Google-Smtp-Source: ABdhPJy5CVwrSpfRhPw00RtBuvbmvtiTNsnmpjnMCPQ6mTw1yTZs90kdBTwdZwETe3ArmExmBZzDAcGFyzLu0CyxgVI= X-Received: by 2002:a2e:1609:: with SMTP id w9mr5346671ljd.90.1633042697541; Thu, 30 Sep 2021 15:58:17 -0700 (PDT) MIME-Version: 1.0 References: <20210915195306.612966-1-kaleshsingh@google.com> In-Reply-To: From: Namhyung Kim Date: Thu, 30 Sep 2021 15:58:06 -0700 Message-ID: Subject: Re: [PATCH 0/5] tracing: Extend histogram triggers expression parsing To: Kalesh Singh Cc: Suren Baghdasaryan , Hridya Valsaraju , Jonathan Corbet , Steven Rostedt , Ingo Molnar , Shuah Khan , Tom Zanussi , Masami Hiramatsu , "open list:DOCUMENTATION" , LKML , "open list:KERNEL SELFTEST FRAMEWORK" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Hi Kalesh, On Wed, Sep 15, 2021 at 1:09 PM Kalesh Singh wrote: > > On Wed, Sep 15, 2021 at 12:53 PM Kalesh Singh wrote: > > > > The frequency of the rss_stat trace event is known to be of the same > > magnitude as that of the sched_switch event on Android devices. This can > > cause flooding of the trace buffer with rss_stat traces leading to a > > decreased trace buffer capacity and loss of data. > > > > If it is not necessary to monitor very small changes in rss (as is the > > case in Android) then the rss_stat tracepoint can be throttled to only > > emit the event once there is a large enough change in the rss size. > > The original patch that introduced the rss_stat tracepoint also proposed > > a fixed throttling mechanism that only emits the rss_stat event > > when the rss size crosses a 512KB boundary. It was concluded that more > > generic support for this type of filtering/throttling was need, so that > > it can be applied to any trace event. [1] > > > > From the discussion in [1], histogram triggers seemed the most likely > > candidate to support this type of throttling. For instance to achieve the > > same throttling as was proposed in [1]: > > > > (1) Create a histogram variable to save the 512KB bucket of the rss size > > (2) Use the onchange handler to generate a synthetic event when the > > rss size bucket changes. > > > > The only missing pieces to support such a hist trigger are: > > (1) Support for setting a hist variable to a specific value -- to set > > the bucket size / granularity. > > (2) Support for division arithmetic operation -- to determine the > > corresponding bucket for an rss size. > > > > This series extends histogram trigger expressions to: > > (1) Allow assigning numeric literals to hist variable (eg. x=1234) > > and using literals directly in expressions (eg. x=size/1234) > > (2) Support division and multiplication in hist expressions. > > (eg. a=$x/$y*z); and > > (3) Fixes expression parsing for non-associative operators: subtraction > > and division. (eg. 8-4-2 should be 2 not 6) > > > > The rss_stat event can then be throttled using histogram triggers as > > below: > > > > # Create a synthetic event to monitor instead of the high frequency > > # rss_stat event > > echo 'rss_stat_throttled unsigned int mm_id; unsigned int curr; > > int member; long size' >> tracing/synthetic_events > > > > # Create a hist trigger that emits the synthetic rss_stat_throttled > > # event only when the rss size crosses a 512KB boundary. > > echo 'hist:keys=common_pid:bucket=size/0x80000:onchange($bucket) > > .rss_stat_throttled(mm_id,curr,member,size)' > > >> events/kmem/rss_stat/trigger > > > > Sorry, I have a clerical mistake here. The above key should be: > s/keys=common_pid/keys=keys=mm_id,member > > The rss size is specific to the mm struct's member not the pid. > The results below were captured with the correct key so no changes there. > > > ------ Test Results ------ > > Histograms can also be used to evaluate the effectiveness of this > > throttling by noting the Total Hits on each trigger: > > > > echo 'hist:keys=common_pid' >> events/sched/sched_switch/trigger > > echo 'hist:keys=common_pid' >> events/kmem/rss_stat/trigger > > echo 'hist:keys=common_pid' > > >> events/synthetic/rss_stat_throttled/trigger > > > > Allowing the above example (512KB granularity) run for 5 minutes on > > an arm64 device with 5.10 kernel: > > > > sched_switch : total hits = 147153 > > rss_stat : total hits = 38863 > > rss_stat_throttled: total hits = 2409 > > > > The synthetic rss_stat_throttled event is ~16x less frequent than the > > rss_stat event when using a 512KB granularity. > > > > > > The results are more pronounced when rss size is changing at a higher > > rate in small increments. For instance the following results were obtained > > by recording the hits on the above events for a run of Android's > > lmkd_unit_test [2], which continually forks processes that map anonymous > > memory until there is an oom kill: > > > > sched_switch : total hits = 148832 > > rss_stat : total hits = 4754802 > > rss_stat_throttled: total hits = 96214 > > > > In this stress this, the synthetic rss_stat_throttled event is ~50x less > > frequent than the rss_stat event when using a 512KB granularity. > > > > > > [1] https://lore.kernel.org/lkml/20190903200905.198642-1-joel@joelfernandes.org/ > > [2] https://cs.android.com/android/platform/superproject/+/master:system/memory/lmkd/tests/lmkd_test.cpp > > > > Signed-off-by: Kalesh Singh Reviewed-by: Namhyung Kim Thanks, Namhyung > > > > Kalesh Singh (5): > > tracing: Add support for creating hist trigger variables from literal > > tracing: Add division and multiplication support for hist triggers > > tracing: Fix operator precedence for hist triggers expression > > tracing/selftests: Add tests for hist trigger expression parsing > > tracing/histogram: Document expression arithmetic and constants > > > > Documentation/trace/histogram.rst | 14 + > > kernel/trace/trace_events_hist.c | 318 +++++++++++++++--- > > .../testing/selftests/ftrace/test.d/functions | 4 +- > > .../trigger/trigger-hist-expressions.tc | 73 ++++ > > 4 files changed, 357 insertions(+), 52 deletions(-) > > create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-expressions.tc > > > > > > base-commit: 3ca706c189db861b2ca2019a0901b94050ca49d8 > > -- > > 2.33.0.309.g3052b89438-goog > >