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=-2.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_MED, URIBL_BLOCKED,USER_AGENT_GIT 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 172FBC43142 for ; Mon, 25 Jun 2018 15:14:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C2AFE208E9 for ; Mon, 25 Jun 2018 15:14:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=toxicpanda-com.20150623.gappssmtp.com header.i=@toxicpanda-com.20150623.gappssmtp.com header.b="ujuLvrpn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C2AFE208E9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=toxicpanda.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935003AbeFYPOT (ORCPT ); Mon, 25 Jun 2018 11:14:19 -0400 Received: from mail-qt0-f195.google.com ([209.85.216.195]:37471 "EHLO mail-qt0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934868AbeFYPNG (ORCPT ); Mon, 25 Jun 2018 11:13:06 -0400 Received: by mail-qt0-f195.google.com with SMTP id a18-v6so12243158qtj.4 for ; Mon, 25 Jun 2018 08:13:05 -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=oGWHcF+I1FAb0T0RllTc5crNDw5hGehwQIUcOHp09k0=; b=ujuLvrpn9ebOxrjRdqiM+INsd8aJOEn/mvet/IPajucCdnrYlfIsYDV9OG1265eNri /byfJUi10fq2pYA6xDQenDfUEW4HyLXtSqk0iRQSBbIR1BP2ppmMYXaNl5geO/9aSHB0 JZybvJ5P0+Eu9LEpU2uR2nED4e+96rMK6wcNDpWVYoyxYEuRDTuzR87DDwEObwO1Vno+ tuv4CrZsTI8LmubWli3HS819fI79wuDqjhv3jo66kPLp8Dpkggx4W8OwRSU+hqXXLff+ 06AwO7rwumanWMBFwUEE0HF5U61J0YR8MDxp11w30sBJWP/R3go+Jut78tkZypaVTOCO DtXA== 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=oGWHcF+I1FAb0T0RllTc5crNDw5hGehwQIUcOHp09k0=; b=S+/qCxLAw7B73x3m4i03Ndx6R/PGbzRZfM8r1bkz4ZoUDfr64CyNSzuWzvVHyfS7hp yeEX9jknOM3XnqBhyOqIYdjBhQwUkrN0fW5GO82sMyXE8hctiVzvySm4KowG5ubsYh2R miUMnBt5ndeQXe1Gqck8V3VdOAHQ181/A4vKfaQDUCAjqgqhVLqCeQPNnmlCcVhOEJbi KbPMdHqWAPGOayQAZ7r/CvBXJBwfgI1ML8evExDUFC/Pmb7uOeiX8z0Mj2Iw4lfPypg6 Ab3mscMZatD6lD9x5wliU3XeWaUQ+KAfbnfD6bRIJ4QNdVCLVDrzm4dS5sPhtsd1ctNK LsKg== X-Gm-Message-State: APt69E3d0WHDA8AIcnbESotZnLTVjehLr12Q6jQzkrUf4mE1f0wcFeUW 3A9VS86pBo9/KefOE0aYHmJJ6A== X-Google-Smtp-Source: AAOMgpcrsTjq904z7XzZ07cIkkorVYYx7ju/v5HPGooWPlF/Z/jIYDnsx6+d4H5/+QmKJm3Mo9cnAw== X-Received: by 2002:a0c:f989:: with SMTP id t9-v6mr11213894qvn.96.1529939585217; Mon, 25 Jun 2018 08:13:05 -0700 (PDT) Received: from localhost ([107.15.81.208]) by smtp.gmail.com with ESMTPSA id g188-v6sm10537703qkc.37.2018.06.25.08.13.04 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 25 Jun 2018 08:13:04 -0700 (PDT) From: Josef Bacik To: axboe@kernel.dk, linux-block@vger.kernel.org, kernel-team@fb.com, akpm@linux-foundation.org, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, tj@kernel.org, linux-fsdevel@vger.kernel.org Cc: Josef Bacik Subject: [PATCH 13/15] Documentation: add a doc for blk-iolatency Date: Mon, 25 Jun 2018 11:12:41 -0400 Message-Id: <20180625151243.2132-14-josef@toxicpanda.com> X-Mailer: git-send-email 2.14.3 In-Reply-To: <20180625151243.2132-1-josef@toxicpanda.com> References: <20180625151243.2132-1-josef@toxicpanda.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Josef Bacik A basic documentation to describe the interface, statistics, and behavior of io.latency. Signed-off-by: Josef Bacik --- Documentation/cgroup-v2.txt | 79 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+) diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt index 74cdeaed9f7a..f6684ec99720 100644 --- a/Documentation/cgroup-v2.txt +++ b/Documentation/cgroup-v2.txt @@ -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 @@ -1395,6 +1398,82 @@ 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 it's +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 it's 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=