From patchwork Wed Sep 15 19:52:44 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kalesh Singh X-Patchwork-Id: 12497295 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=-26.2 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_AGENT_GIT,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 AB88CC433FE for ; Wed, 15 Sep 2021 19:53:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7AA9A61056 for ; Wed, 15 Sep 2021 19:53:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231559AbhIOTyj (ORCPT ); Wed, 15 Sep 2021 15:54:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50330 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229732AbhIOTyj (ORCPT ); Wed, 15 Sep 2021 15:54:39 -0400 Received: from mail-qt1-x849.google.com (mail-qt1-x849.google.com [IPv6:2607:f8b0:4864:20::849]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C4E57C061575 for ; Wed, 15 Sep 2021 12:53:19 -0700 (PDT) Received: by mail-qt1-x849.google.com with SMTP id f34-20020a05622a1a2200b0029c338949c1so6659256qtb.8 for ; Wed, 15 Sep 2021 12:53:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:message-id:mime-version:subject:from:cc; bh=ZN8L1SRgYQneOokAyF/YDPfiVZ2ZJf5kUNPTEXGrDyM=; b=oOWHam1LZ3eZVZuUUKQnwIZD45mGvoGWhDIGGcaJ/ZVuaxJgr9C12nV1IedLU0nJUK rPAvCc0ieMBeNadMOasQbF021ZURMfXk3HM1Hx28jK9CP0R9rAiqoXXBWM2zoPdrFZx5 5CIEkMxg5A7eeCUu5e7QpVjIo50IneSZIba6f7dwTlDzcMSqUnTCLUs8t8GNYWz1RirZ gZ1O5YVjciLF2y565msC2T0fJe/tyM8XRS1SxvHRKdzAt9PbzKEUaNXz1RheFKUK+x/L Yv5GsRq+7WsmVaMUo2k83oTrKFmm+N/ujJBzn6NIFv+tXxi8JPdqdAdhBNfPUitdZm3L ewvg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:cc; bh=ZN8L1SRgYQneOokAyF/YDPfiVZ2ZJf5kUNPTEXGrDyM=; b=1b1rZG98wdnSbVH58vFZ3XV6Eg4s43P0+trL72s0PhfC4xntIfhBwoa8vDZ/pqsk6b nXGsMfFap6W3G6ooJXuW3tWGcA7HpZnvUDJeEXIALAtZlaT7qjUPZhiOSgJz4RtejpDn QFxayX9axjtEk+/xtrXrtbY5vL8zhh+QsUGQORKLTUogiMPZMw8z/ZGlKyTsnQcnqHUg eIyg9qTJV96oQd+TRfVcWmYNpUl0l39mjbQydrQ2nmXh5HNruLiwStejlaTns+kRnfal twiT4xStmDVHL6i6l9Y691J6Xsqc7y7u9meNsHttaV+tKT7NK4Q+QPKPUZ+3eQlrcXix GlYA== X-Gm-Message-State: AOAM531YeAzXaJEIItuc1z/kPMVaK9CGPu6dyyqWJiWYWpFVDCqlXGgP 5g3hw6m4zuAQqnGPmIrDNvk8Fu7wNFrV5AVb7w== X-Google-Smtp-Source: ABdhPJyi27fA7iU5UGtpeuYB5pqLFXaWsK5XRc4GI4VOmjlh0qYYnWCd1v1FR24xxOzz+cwyWWbIz0v2Qb/QaMlZlQ== X-Received: from kaleshsingh.c.googlers.com ([fda3:e722:ac3:cc00:14:4d90:c0a8:2145]) (user=kaleshsingh job=sendgmr) by 2002:a05:6214:13e9:: with SMTP id ch9mr1497532qvb.45.1631735598972; Wed, 15 Sep 2021 12:53:18 -0700 (PDT) Date: Wed, 15 Sep 2021 19:52:44 +0000 Message-Id: <20210915195306.612966-1-kaleshsingh@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.33.0.309.g3052b89438-goog Subject: [PATCH 0/5] tracing: Extend histogram triggers expression parsing From: Kalesh Singh Cc: surenb@google.com, hridya@google.com, namhyung@kernel.org, Kalesh Singh , Jonathan Corbet , Steven Rostedt , Ingo Molnar , Shuah Khan , Tom Zanussi , Masami Hiramatsu , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org To: unlisted-recipients:; (no To-header on input) Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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 ------ 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 Reviewed-by: Namhyung Kim