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=-17.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 2A11FC43331 for ; Wed, 1 Apr 2020 23:40:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E91C820719 for ; Wed, 1 Apr 2020 23:40:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ANRbvwnG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387446AbgDAXkd (ORCPT ); Wed, 1 Apr 2020 19:40:33 -0400 Received: from mail-qt1-f201.google.com ([209.85.160.201]:55562 "EHLO mail-qt1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387406AbgDAXkc (ORCPT ); Wed, 1 Apr 2020 19:40:32 -0400 Received: by mail-qt1-f201.google.com with SMTP id o10so1490394qtk.22 for ; Wed, 01 Apr 2020 16:40:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=IJbUqAZoaZbcftRq/6j3id1/PIehiPTgOI+a+J70oz0=; b=ANRbvwnGcWbAdfV/0DjJdBoS7WfxjOUDLjkOX9FtAUuCLbTkQc5Vm8o6ng/9PBOcUY L6MzCBafGFHQFw0rNrH4auccGNPaPKJNj+HpgTHoBWXw7BQjkZfJIHTbYJ6sZ0BA9S3F O6Vn/WOdYUJgQQLy63630NocVAVp9jwoCH4XrQH+/Fv5R1aKyB3lxsyIqCX1tUrpJwj0 Qi+KwVhq0Slp3zyedKe2fB9ucOgRqCCUdONtXtPmT1r6OHeb0SdjyW9B1WjDT4e5TZPV 2myHWCmxlbzh/TkmW60y51EO559ilCvJOjt5rQHupor2MTeFh3WLhaSrOLLXq/3CpZrJ ZRuw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=IJbUqAZoaZbcftRq/6j3id1/PIehiPTgOI+a+J70oz0=; b=IJUUzrpfuEHvscovIzokYi6qFzysKkzA3SJQCTS/oiBVsu4hnZm9UtoVcRiJ1Xgpiz Cuef/5ZOaQ27sjLLS0we99KAGPxhyRQ06RVio9XiKkiqvZvzcMx9+hx513kaAxpzpYLk oBbUf865jfMMrvYY7bZ8oX+04WnX4VNeun284+kd/US+2ETKMvWU5yDEEsXa0rGh8XQi /i9uJ3E//+JQR+REEJTwdfT5foH6sv/b/AxexAUhAgicr6Nsc7A2TcovnWCU8hvZJFEI fg8imMDfxgPnCMRmeJYK/idfK+sFl/8wOxzyexEVWxXI8p175stz8wqsSHjk9daau2e/ xlgA== X-Gm-Message-State: AGi0PubAPnhmCxWsIThL2Ryp6RVSS9FbNzGSlO5rAFmTPu9craK62rBk p9RC+unHNC4eerEVmRPEzP7WGWsjHV07 X-Google-Smtp-Source: APiQypJj1nzy0xxZiK/ancIXb99LI/aD6DB8ovIp38LT8P7v9l2KUFKyZzm4EK63vqAlR6TV4bnqFDCVobNf X-Received: by 2002:a05:6214:2c4:: with SMTP id g4mr618723qvu.65.1585784430080; Wed, 01 Apr 2020 16:40:30 -0700 (PDT) Date: Wed, 1 Apr 2020 16:39:42 -0700 In-Reply-To: <20200401233945.133550-1-irogers@google.com> Message-Id: <20200401233945.133550-3-irogers@google.com> Mime-Version: 1.0 References: <20200401233945.133550-1-irogers@google.com> X-Mailer: git-send-email 2.26.0.rc2.310.g2932bb562d-goog Subject: [PATCH 2/5] tools api fs: make xxx__mountpoint() more scalable From: Ian Rogers To: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , 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 Cc: Stephane Eranian , Ian Rogers Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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