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 X-Spam-Level: X-Spam-Status: No, score=-23.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BAAE9C433F5 for ; Wed, 15 Sep 2021 20:09:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9B0C6611C4 for ; Wed, 15 Sep 2021 20:09:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231751AbhIOULD (ORCPT ); Wed, 15 Sep 2021 16:11:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54082 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231628AbhIOULC (ORCPT ); Wed, 15 Sep 2021 16:11:02 -0400 Received: from mail-pf1-x433.google.com (mail-pf1-x433.google.com [IPv6:2607:f8b0:4864:20::433]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8F703C061575 for ; Wed, 15 Sep 2021 13:09:43 -0700 (PDT) Received: by mail-pf1-x433.google.com with SMTP id j16so3780849pfc.2 for ; Wed, 15 Sep 2021 13:09:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:cc; bh=GOFLBCpd5YWd1LKYoUMXIDX6I2Oh8/PMBaNyH9Apy8s=; b=tbeHY6HSKONX1dnJiDe351BSWmDCLLTCkD9kCFP14uCRb6r4Q+5A+ads+3HOy15ufC zawzsbMA90aBBKAnWnB1gREvqvmgDkmSRQgbInRAuBRT+Fm3Dd2GCj9Tcc+4kTRiDl+K GZSFedSCBTkgmkr/sWEEBXix+M7tqAITnrYH0GIwxXavUF8/WPXiu9wZFZIuOJZ5+XkC UhGDyl9mnez3aIB7I6OO2iouSyEGL5tuq7AvXKX/uv6WzdQQd7OvDz22OkyK7Ubo1kGI 7djGTnpP2LsEUHjjFR8tjo3UWojxmON+gnq3WqIUInv/bcN6MslS5MCgmMTg0PreDuSL qWpw== 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:cc; bh=GOFLBCpd5YWd1LKYoUMXIDX6I2Oh8/PMBaNyH9Apy8s=; b=BjT2qFBqOmlUGXvQ/dkqHER+bZAMuW+InUuXZsL6WGZzsZrMZkCkAv0MuA3QGBXvi0 iuLqwovJkzCXaa4mSDfAWkNvuiaLoU/n/i0RcXuBt7MG9iPnnJqAlvAfrGetFGeSs6QR sXv7+/YMr0gUO1zVBAiH2KIAHw1gTAaKINm5rCD/cEFmuSolEiGlMJ/o+pOC/hFNZ1cX ssplyhfWO95DF1SVX0TKp+XOv9VzcTtuQcmnsd0YLha5uMBP7/3eBs6x9o8tabaJ6cqr PRF1my76/Hp3+gP2ogdTeZucFyJoZAfgsEscGREi/Kr+MEtUE36La3MFuUV0fhQVVVBx Id5A== X-Gm-Message-State: AOAM532rgR5DdX5rMxA2YeU9oRtv60TT4/QdAJhnyhwfZMoxo7OX5SP7 sfLCO9Af0QMre7bcgGmRSHtO5NkRlVZB+MxZUDc/QGI/ML5MjQ== X-Received: by 2002:a63:7a10:: with SMTP id v16mt1174071pgc.146.1631736582785; Wed, 15 Sep 2021 13:09:42 -0700 (PDT) MIME-Version: 1.0 References: <20210915195306.612966-1-kaleshsingh@google.com> In-Reply-To: <20210915195306.612966-1-kaleshsingh@google.com> From: Kalesh Singh Date: Wed, 15 Sep 2021 13:09:31 -0700 Message-ID: Subject: Re: [PATCH 0/5] tracing: Extend histogram triggers expression parsing Cc: Suren Baghdasaryan , Hridya Valsaraju , namhyung@kernel.org, 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" To: unlisted-recipients:; (no To-header on input) Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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 > > 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 >