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=-6.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 6A6A3C2BA19 for ; Mon, 6 Apr 2020 14:07:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 351C5238E1 for ; Mon, 6 Apr 2020 14:07:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CCDK7E1R" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728632AbgDFOH0 (ORCPT ); Mon, 6 Apr 2020 10:07:26 -0400 Received: from mail-qk1-f196.google.com ([209.85.222.196]:44589 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726436AbgDFOHZ (ORCPT ); Mon, 6 Apr 2020 10:07:25 -0400 Received: by mail-qk1-f196.google.com with SMTP id j4so16162347qkc.11; Mon, 06 Apr 2020 07:07:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=hN2xuaWsyNjCaRF45tyR+htCYnhC3ctmM5qosC2W1ic=; b=CCDK7E1RL7p0En992jjqkCglKva7goplCRdB4BdqVNaIVfEgl3bX4XS8/gNqjuWu0f jET/osdhjj42ToJ6aX+zhoj3Mne/yOvRj2FktxYl9lvgdVYPa1G6gjZcvCbEwc7FcvC0 YXd/Nrov5r3h+T47LE9L8WO5/bj96aw+YvCO1lMVy6gcINApjwb5u044MhLs9GnIrJ3N /h4v0XmX3Jl1tBhfM/CANqfGO6xQFAO/qxTSbOBbdnv8bZoMjGepEzD6gk1OmzdwGo74 N6PQ2avCvE3wf7N713A4WiZ9Mkpqt+8DUICUKZ7cb4+SWkRpGbWcKntJok/RvBpVgG5M QBbw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=hN2xuaWsyNjCaRF45tyR+htCYnhC3ctmM5qosC2W1ic=; b=DcpJOOKBgejPQK//+Fd9TjFbfMbEKyLtNU9VkpstQMQLcQ8bUMaXMCdqdnwr9+gfDz eH2wzrXsaGUKq/eQAhcZXdMR607YrXAW46Jg/4GVD4Cp3bHhwCP37UKtw/cd6PyPH95h Vxh5duZj4Jwj1hHU8jB1CuzFGkGHJK+3ivmF+DZjAHEw9JANxSe1lZgh2QkhluiZK+zV my2A7DTCkh6HeseWvDOUpqb4Q40auDR+berc4o7Bg6/aWIxmPajJGKPG5SLTZcxoIRFW qLmGypbZoSR3eSO/g6tsGplVgSET35s4TlqBoaTzdu3IU270TwTIfPNSFcCWgxzSSKyG LY1A== X-Gm-Message-State: AGi0PuaSGI2WUfMpbY6j8SvkWpcvY9WrrwJiq+U0pHQZq3OYiIUjWUXe zi50OV+l9E+K58GET4piII8= X-Google-Smtp-Source: APiQypIMgXkLRmmCyWPPftDbEDqk0uI4xOgR9pUBKnuzhHgs47m9J+4V4PG9OUtfzbVWOcRkp14oAQ== X-Received: by 2002:a05:620a:1019:: with SMTP id z25mr21823801qkj.479.1586182043992; Mon, 06 Apr 2020 07:07:23 -0700 (PDT) Received: from quaco.ghostprotocols.net ([179.97.37.151]) by smtp.gmail.com with ESMTPSA id x24sm2472202qth.80.2020.04.06.07.07.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Apr 2020 07:07:23 -0700 (PDT) From: Arnaldo Carvalho de Melo X-Google-Original-From: Arnaldo Carvalho de Melo Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id 5B73C409A3; Mon, 6 Apr 2020 11:07:21 -0300 (-03) Date: Mon, 6 Apr 2020 11:07:21 -0300 To: Ian Rogers Cc: Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Petr Mladek , Andrey Zhizhikin , Kefeng Wang , Thomas Gleixner , Kan Liang , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Stephane Eranian Subject: Re: [PATCH v2 2/5] tools api fs: make xxx__mountpoint() more scalable Message-ID: <20200406140721.GD29826@kernel.org> References: <20200402154357.107873-1-irogers@google.com> <20200402154357.107873-3-irogers@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200402154357.107873-3-irogers@google.com> X-Url: http://acmel.wordpress.com Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Thu, Apr 02, 2020 at 08:43:54AM -0700, Ian Rogers escreveu: > From: Stephane Eranian > > The xxx_mountpoint() interface provided by fs.c finds > mount points for common pseudo filesystems. The first > time xxx_mountpoint() is invoked, it scans the mount > table (/proc/mounts) looking for a match. If found, it > is cached. The price to scan /proc/mounts is paid once > if the mount is found. > > When the mount point is not found, subsequent calls to > xxx_mountpoint() scan /proc/mounts over and over again. > There is no caching. Thanks, applied, lets see if someone screams... - Arnaldo > This causes a scaling issue in perf record with hugeltbfs__mountpoint(). > The function is called for each process found in synthesize__mmap_events(). > If the machine has thousands of processes and if the /proc/mounts has many > entries this could cause major overhead in perf record. We have observed > multi-second slowdowns on some configurations. > > As an example on a laptop: > > Before: > $ sudo umount /dev/hugepages > $ strace -e trace=openat -o /tmp/tt perf record -a ls > $ fgrep mounts /tmp/tt > 285 > > After: > $ sudo umount /dev/hugepages > $ strace -e trace=openat -o /tmp/tt perf record -a ls > $ fgrep mounts /tmp/tt > 1 > > One could argue that the non-caching in case the moint point is not found > is intentional. That way subsequent calls may discover a moint point if > the sysadmin mounts the filesystem. But the same argument could be made > against caching the mount point. It could be unmounted causing errors. > It all depends on the intent of the interface. This patch assumes it > is expected to scan /proc/mounts once. The patch documents the caching > behavior in the fs.h header file. > > An alternative would be to just fix perf record. But it would solve > the problem with hugetlbs__mountpoint() but there could be similar > issues (possibly down the line) with other xxx_mountpoint() calls > in perf or other tools. > > Signed-off-by: Stephane Eranian > Reviewed-by: Ian Rogers > Acked-by: Jiri Olsa > Signed-off-by: Ian Rogers > --- > tools/lib/api/fs/fs.c | 17 +++++++++++++++++ > tools/lib/api/fs/fs.h | 12 ++++++++++++ > 2 files changed, 29 insertions(+) > > diff --git a/tools/lib/api/fs/fs.c b/tools/lib/api/fs/fs.c > index 027b18f7ed8c..82f53d81a7a7 100644 > --- a/tools/lib/api/fs/fs.c > +++ b/tools/lib/api/fs/fs.c > @@ -90,6 +90,7 @@ struct fs { > const char * const *mounts; > char path[PATH_MAX]; > bool found; > + bool checked; > long magic; > }; > > @@ -111,31 +112,37 @@ static struct fs fs__entries[] = { > .name = "sysfs", > .mounts = sysfs__fs_known_mountpoints, > .magic = SYSFS_MAGIC, > + .checked = false, > }, > [FS__PROCFS] = { > .name = "proc", > .mounts = procfs__known_mountpoints, > .magic = PROC_SUPER_MAGIC, > + .checked = false, > }, > [FS__DEBUGFS] = { > .name = "debugfs", > .mounts = debugfs__known_mountpoints, > .magic = DEBUGFS_MAGIC, > + .checked = false, > }, > [FS__TRACEFS] = { > .name = "tracefs", > .mounts = tracefs__known_mountpoints, > .magic = TRACEFS_MAGIC, > + .checked = false, > }, > [FS__HUGETLBFS] = { > .name = "hugetlbfs", > .mounts = hugetlbfs__known_mountpoints, > .magic = HUGETLBFS_MAGIC, > + .checked = false, > }, > [FS__BPF_FS] = { > .name = "bpf", > .mounts = bpf_fs__known_mountpoints, > .magic = BPF_FS_MAGIC, > + .checked = false, > }, > }; > > @@ -158,6 +165,7 @@ static bool fs__read_mounts(struct fs *fs) > } > > fclose(fp); > + fs->checked = true; > return fs->found = found; > } > > @@ -220,6 +228,7 @@ static bool fs__env_override(struct fs *fs) > return false; > > fs->found = true; > + fs->checked = true; > strncpy(fs->path, override_path, sizeof(fs->path) - 1); > fs->path[sizeof(fs->path) - 1] = '\0'; > return true; > @@ -246,6 +255,14 @@ static const char *fs__mountpoint(int idx) > if (fs->found) > return (const char *)fs->path; > > + /* the mount point was already checked for the mount point > + * but and did not exist, so return NULL to avoid scanning again. > + * This makes the found and not found paths cost equivalent > + * in case of multiple calls. > + */ > + if (fs->checked) > + return NULL; > + > return fs__get_mountpoint(fs); > } > > diff --git a/tools/lib/api/fs/fs.h b/tools/lib/api/fs/fs.h > index 936edb95e1f3..aa222ca30311 100644 > --- a/tools/lib/api/fs/fs.h > +++ b/tools/lib/api/fs/fs.h > @@ -18,6 +18,18 @@ > const char *name##__mount(void); \ > bool name##__configured(void); \ > > +/* > + * The xxxx__mountpoint() entry points find the first match mount point for each > + * filesystems listed below, where xxxx is the filesystem type. > + * > + * The interface is as follows: > + * > + * - If a mount point is found on first call, it is cached and used for all > + * subsequent calls. > + * > + * - If a mount point is not found, NULL is returned on first call and all > + * subsequent calls. > + */ > FS(sysfs) > FS(procfs) > FS(debugfs) > -- > 2.26.0.rc2.310.g2932bb562d-goog > -- - Arnaldo