From patchwork Tue Jul 3 15:15:02 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Josef Bacik X-Patchwork-Id: 10504397 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 0A28060325 for ; Tue, 3 Jul 2018 15:16:56 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id EE040289C2 for ; Tue, 3 Jul 2018 15:16:55 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id EB02B28B50; Tue, 3 Jul 2018 15:16:55 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 7C50A28B5A for ; Tue, 3 Jul 2018 15:16:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934119AbeGCPP7 (ORCPT ); Tue, 3 Jul 2018 11:15:59 -0400 Received: from mail-qt0-f195.google.com ([209.85.216.195]:33828 "EHLO mail-qt0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934120AbeGCPP2 (ORCPT ); Tue, 3 Jul 2018 11:15:28 -0400 Received: by mail-qt0-f195.google.com with SMTP id m13-v6so1876085qth.1 for ; Tue, 03 Jul 2018 08:15:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=toxicpanda-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=YsNSDaMPA55NV6tYVklfnMwegywAAoI3iEit0/l5+2A=; b=VxN5gddZ64mTCTUQWkuS46wK/b1oDOvID/LFzpV2u8kdjpKRLh4b5wPkyqnk9derKW rHoGtt3vW2+XtikpgQcMPZsCbOBPzkR6AmltYc6l28NJM9KpViUQKZLoukcEi1f08AVp sp+HF3JifCiCjLjLnB/2fdUzGET7/5ujPU6UAz0jklJS6lV5qOpjccJrlYjdvhsQoZ7s SRmhg8AqmdC45bEvN3lyZ201aPjOxM1HAz1cf81BH+QSnqZX+PZ0w4DiyVp5CTWkD3JM k9H3ih5dtGw8NNY5yFl/PCLJgNhkwGZB6RXiGvui2qaF6MFI1U5v4feWMqgDpiQJ383i CY2g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=YsNSDaMPA55NV6tYVklfnMwegywAAoI3iEit0/l5+2A=; b=huT6T6ykOOozDLx9xLsG7h59W3EV5S5CG4lDA0+PbCFsWrmRj/qEDpkUKCtQbKK8rH TqmVTNAAY5XK4TuixdEOeeMcB8tMSz3/FvfbydX15tvC82ltgqIHzir4yMwKKszcIBAI KWH225xT3JYhZU7ftfyFFP+mVDrv5utpCCx3ZOeZSRmN6I3qmbvzkn7qc3iFsRbEgZMX 3bJ+ODU+XovQeF2Ko1DoPlBv3nBUGMmDlIiQJ7FjN+llUaI5x5+csIMNipxkWZMVXN+R MyyQtsTTYA/2eIm8xaH1aPDQtgndVDFVYd5ip4eDPFNB3FfToavhRuRzwLhHRZJuqRVs wVew== X-Gm-Message-State: APt69E0gIsrpmLXWUmedtcewXOGWXNgEBOoqjt1/hgiEW7q1/nPZ9Iyo bLXNnOj1+iy0f35BGG9SZ7D+vg== X-Google-Smtp-Source: AAOMgpdp+VxCgleNtMxMZpOClY7HS8ickDeDsZBgAADI2YNULl+c6VGOwVpXL3DqxAs5ojnZhN9Wcw== X-Received: by 2002:ac8:2463:: with SMTP id d32-v6mr18392998qtd.41.1530630927787; Tue, 03 Jul 2018 08:15:27 -0700 (PDT) Received: from localhost ([107.15.81.208]) by smtp.gmail.com with ESMTPSA id 16-v6sm817680qkd.93.2018.07.03.08.15.26 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 03 Jul 2018 08:15:26 -0700 (PDT) From: Josef Bacik To: axboe@kernel.dk, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, hannes@cmpxchg.org, tj@kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, kernel-team@fb.com Cc: Josef Bacik Subject: [PATCH 13/14] Documentation: add a doc for blk-iolatency Date: Tue, 3 Jul 2018 11:15:02 -0400 Message-Id: <20180703151503.2549-14-josef@toxicpanda.com> X-Mailer: git-send-email 2.14.3 In-Reply-To: <20180703151503.2549-1-josef@toxicpanda.com> References: <20180703151503.2549-1-josef@toxicpanda.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Josef Bacik A basic documentation to describe the interface, statistics, and behavior of io.latency. Signed-off-by: Josef Bacik --- Documentation/admin-guide/cgroup-v2.rst | 79 +++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 8a2c52d5c53b..569ce27b85e5 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -51,6 +51,9 @@ v1 is available under Documentation/cgroup-v1/. 5-3. IO 5-3-1. IO Interface Files 5-3-2. Writeback + 5-3-3. IO Latency + 5-3-3-1. How IO Latency Throttling Works + 5-3-3-2. IO Latency Interface Files 5-4. PID 5-4-1. PID Interface Files 5-5. Device @@ -1446,6 +1449,82 @@ writeback as follows. vm.dirty[_background]_ratio. +IO Latency +~~~~~~~~~~ + +This is a cgroup v2 controller for IO workload protection. You provide a group +with a latency target, and if the average latency exceeds that target the +controller will throttle any peers that have a lower latency target than the +protected workload. + +The limits are only applied at the peer level in the hierarchy. This means that +in the diagram below, only groups A, B, and C will influence each other, and +groups D and F will influence each other. Group G will influence nobody. + + [root] + / | \ + A B C + / \ | + D F G + + +So the ideal way to configure this is to set io.latency in groups A, B, and C. +Generally you do not want to set a value lower than the latency your device +supports. Experiment to find the value that works best for your workload. +Start at higher than the expected latency for your device and watch the +total_lat_avg value in io.stat for your workload group to get an idea of the +latency you see during normal operation. Use this value as a basis for your +real setting, setting at 10-15% higher than the value in io.stat. +Experimentation is key here because total_lat_avg is a running total, so is the +"statistics" portion of "lies, damned lies, and statistics." + +How IO Latency Throttling Works +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +io.latency is work conserving; so as long as everybody is meeting their latency +target the controller doesn't do anything. Once a group starts missing its +target it begins throttling any peer group that has a higher target than itself. +This throttling takes 2 forms: + +- Queue depth throttling. This is the number of outstanding IO's a group is + allowed to have. We will clamp down relatively quickly, starting at no limit + and going all the way down to 1 IO at a time. + +- Artificial delay induction. There are certain types of IO that cannot be + throttled without possibly adversely affecting higher priority groups. This + includes swapping and metadata IO. These types of IO are allowed to occur + normally, however they are "charged" to the originating group. If the + originating group is being throttled you will see the use_delay and delay + fields in io.stat increase. The delay value is how many microseconds that are + being added to any process that runs in this group. Because this number can + grow quite large if there is a lot of swapping or metadata IO occurring we + limit the individual delay events to 1 second at a time. + +Once the victimized group starts meeting its latency target again it will start +unthrottling any peer groups that were throttled previously. If the victimized +group simply stops doing IO the global counter will unthrottle appropriately. + +IO Latency Interface Files +~~~~~~~~~~~~~~~~~~~~~~~~~~ + + io.latency + This takes a similar format as the other controllers. + + "MAJOR:MINOR target=