From patchwork Wed Oct 20 01:31:37 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kalesh Singh X-Patchwork-Id: 12571479 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 0F3B8C433F5 for ; Wed, 20 Oct 2021 01:33:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E294C610D0 for ; Wed, 20 Oct 2021 01:33:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229663AbhJTBft (ORCPT ); Tue, 19 Oct 2021 21:35:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46212 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229555AbhJTBft (ORCPT ); Tue, 19 Oct 2021 21:35:49 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2E9EC06161C for ; Tue, 19 Oct 2021 18:33:35 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id j193-20020a2523ca000000b005b789d71d9aso27783427ybj.21 for ; Tue, 19 Oct 2021 18:33:35 -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=/oNbKuNJ/NjBt3tvnnNN1bQs/FW9O8UfHJkwZ8aGpZU=; b=M+Jr9PYocMzl6Julf6MHH8OFUtoGTsZ6C2FC9ZjP1oLOhPs842mxdaStpR/DbNmFJV qTAXIcUAYNodjHS9JhdZvBPqEoD4vv/+Kucw9SZhVA/69GiniAGs9w8CpAPtC55yPIxO olhLgmFjZpfAhfD7cpghWOZinz7pJUrNx99NWWjgltjEjNIQ1xM/0NHUdcwk/ZfoAJz5 gbmg88R62x0cu4BU0S+98i9qHaWvw6C1TuqVKnr9PIEBxelaeb/6VSozoNu1Shwl2z89 b/rFwrIT98z538zjqI02P5Jd2hHBxOdaKdCrkWI86s1vhuK3VaWFKslF0dVuCdvOSMK2 sQ1w== 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=/oNbKuNJ/NjBt3tvnnNN1bQs/FW9O8UfHJkwZ8aGpZU=; b=sw9eTiAf6HrSFzUKsMgYMelFr/N86WY4IpQ7b54jKtqu+L/RJg12EHtuDfp/HtQeAf rmWn1UT4mco6TDvOKePQB6oQZ1sMgt0GhHbMHvgMPzI9NmaZUZAGdvuiGEwFF3C5diLL 8+2uNiqWKq3RnQqK3RxUd/PsNKxVyDvZ3jVSeRcxZhyL2goZueZTh4D7C1o26QsuISoA KAfgNf6d6vv1RgPfJr+oWemVTXUMP2k6JZz2QObXTt2dzSOWfQwnfI2d7WFuUOGu2wnT oYPYlNrvcrVkuPad3afKzIzj0hhYTBOruVjoCZUXJu4sDSONd0MTEedm3RX1aSJkgMgd YU/g== X-Gm-Message-State: AOAM533995XzIb7WHKkQ5/Rm2wWGoq4KKi4kQFoyZtuqoSYsiBHAI6xZ QK9uNRVnabclo5N1QwAlvaPw0Hv54oOIN7yKXg== X-Google-Smtp-Source: ABdhPJx8xkUizpCZjRlUmsBfpykOEkGUKPa4YE8/chpH8tDveWIr3wf26Nf0Ec8J5Y45sqxmmgi3UvjEKL8DgEp3Yg== X-Received: from kaleshsingh.mtv.corp.google.com ([2620:15c:211:200:1953:b886:7a6c:bf0]) (user=kaleshsingh job=sendgmr) by 2002:a25:3487:: with SMTP id b129mr36817302yba.249.1634693614938; Tue, 19 Oct 2021 18:33:34 -0700 (PDT) Date: Tue, 19 Oct 2021 18:31:37 -0700 Message-Id: <20211020013153.4106001-1-kaleshsingh@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.33.0.1079.g6e70778dc9-goog Subject: [PATCH v2 0/5] tracing: Extend histogram triggers expression parsing From: Kalesh Singh Cc: surenb@google.com, hridya@google.com, namhyung@kernel.org, kernel-team@android.com, Kalesh Singh , Jonathan Corbet , Steven Rostedt , Ingo Molnar , Shuah Khan , Masami Hiramatsu , Tom Zanussi , 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 Hi all, The v1 of this series was posted at: https://lore.kernel.org/r/20210915195306.612966-1-kaleshsingh@google.com/ The cover letter here is mostly identical to that in v1, with a correction to how the results were obtained. --- 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=mm_id,member: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 test, 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 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 | 74 ++++ 4 files changed, 358 insertions(+), 52 deletions(-) create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-expressions.tc base-commit: d9abdee5fd5abffd0e763e52fbfa3116de167822