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=-6.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 14B2AC10DCE for ; Tue, 24 Mar 2020 06:39:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D3D5D20714 for ; Tue, 24 Mar 2020 06:39:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b="lNECZX3P" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727345AbgCXGjq (ORCPT ); Tue, 24 Mar 2020 02:39:46 -0400 Received: from forwardcorp1p.mail.yandex.net ([77.88.29.217]:49244 "EHLO forwardcorp1p.mail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725867AbgCXGjq (ORCPT ); Tue, 24 Mar 2020 02:39:46 -0400 Received: from mxbackcorp1o.mail.yandex.net (mxbackcorp1o.mail.yandex.net [IPv6:2a02:6b8:0:1a2d::301]) by forwardcorp1p.mail.yandex.net (Yandex) with ESMTP id C15512E14E6; Tue, 24 Mar 2020 09:39:41 +0300 (MSK) Received: from myt5-70c90f7d6d7d.qloud-c.yandex.net (myt5-70c90f7d6d7d.qloud-c.yandex.net [2a02:6b8:c12:3e2c:0:640:70c9:f7d]) by mxbackcorp1o.mail.yandex.net (mxbackcorp/Yandex) with ESMTP id Yu48TXQ3BV-deAWexTD; Tue, 24 Mar 2020 09:39:41 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1585031981; bh=9BXr/kPTT7SbrhXNKVRApkET1ZIi+QckpVvhmXhFv9A=; h=In-Reply-To:Message-ID:References:Date:To:From:Subject:Cc; b=lNECZX3PhPjgiVsoGg6RcNi2J+qLWkTyOL6vvyAhTvLtT0eTvtHNdfsy1I9dMsWWj PnkXsYJA6IkDA3Uk1Gm9LFWm8Fmxe0n+am8vPF37yHlg8L5DuqqZ/AB7RJ54Pgxsox WEL0yQTiBZLH3iXFufpWdGVUi47t/JPuxwB0UyUk= Authentication-Results: mxbackcorp1o.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Received: from unknown (unknown [2a02:6b8:b080:6410::1:2]) by myt5-70c90f7d6d7d.qloud-c.yandex.net (smtpcorp/Yandex) with ESMTPSA id B0rSjocyNB-deb8Twhk; Tue, 24 Mar 2020 09:39:40 +0300 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client certificate not present) Subject: [PATCH v3 1/3] block/diskstats: more accurate approximation of io_ticks for slow disks From: Konstantin Khlebnikov To: linux-block@vger.kernel.org, Jens Axboe , linux-kernel@vger.kernel.org Cc: Mikulas Patocka , Mike Snitzer , Ming Lei Date: Tue, 24 Mar 2020 09:39:40 +0300 Message-ID: <158503198072.1955.16227279292140721351.stgit@buzz> In-Reply-To: <158503038812.1955.7827988255138056389.stgit@buzz> References: <158503038812.1955.7827988255138056389.stgit@buzz> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Currently io_ticks is approximated by adding one at each start and end of requests if jiffies counter has changed. This works perfectly for requests shorter than a jiffy or if one of requests starts/ends at each jiffy. If disk executes just one request at a time and they are longer than two jiffies then only first and last jiffies will be accounted. Fix is simple: at the end of request add up into io_ticks jiffies passed since last update rather than just one jiffy. Example: common HDD executes random read 4k requests around 12ms. fio --name=test --filename=/dev/sdb --rw=randread --direct=1 --runtime=30 & iostat -x 10 sdb Note changes of iostat's "%util" 8,43% -> 99,99% before/after patch: Before: Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util sdb 0,00 0,00 82,60 0,00 330,40 0,00 8,00 0,96 12,09 12,09 0,00 1,02 8,43 After: Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util sdb 0,00 0,00 82,50 0,00 330,00 0,00 8,00 1,00 12,10 12,10 0,00 12,12 99,99 For load estimation "%util" is not as useful as average queue length, but it clearly shows how often disk queue is completely empty. Fixes: 5b18b5a73760 ("block: delete part_round_stats and switch to less precise counting") Signed-off-by: Konstantin Khlebnikov --- Documentation/admin-guide/iostats.rst | 5 ++++- block/bio.c | 8 ++++---- block/blk-core.c | 4 ++-- include/linux/genhd.h | 2 +- 4 files changed, 11 insertions(+), 8 deletions(-) diff --git a/Documentation/admin-guide/iostats.rst b/Documentation/admin-guide/iostats.rst index df5b8345c41d..9b14b0c2c9c4 100644 --- a/Documentation/admin-guide/iostats.rst +++ b/Documentation/admin-guide/iostats.rst @@ -100,7 +100,7 @@ Field 10 -- # of milliseconds spent doing I/Os (unsigned int) Since 5.0 this field counts jiffies when at least one request was started or completed. If request runs more than 2 jiffies then some - I/O time will not be accounted unless there are other requests. + I/O time might be not accounted in case of concurrent requests. Field 11 -- weighted # of milliseconds spent doing I/Os (unsigned int) This field is incremented at each I/O start, I/O completion, I/O @@ -143,6 +143,9 @@ are summed (possibly overflowing the unsigned long variable they are summed to) and the result given to the user. There is no convenient user interface for accessing the per-CPU counters themselves. +Since 4.19 request times are measured with nanoseconds precision and +truncated to milliseconds before showing in this interface. + Disks vs Partitions ------------------- diff --git a/block/bio.c b/block/bio.c index 0985f3422556..b1053eb7af37 100644 --- a/block/bio.c +++ b/block/bio.c @@ -1762,14 +1762,14 @@ void bio_check_pages_dirty(struct bio *bio) schedule_work(&bio_dirty_work); } -void update_io_ticks(struct hd_struct *part, unsigned long now) +void update_io_ticks(struct hd_struct *part, unsigned long now, bool end) { unsigned long stamp; again: stamp = READ_ONCE(part->stamp); if (unlikely(stamp != now)) { if (likely(cmpxchg(&part->stamp, stamp, now) == stamp)) { - __part_stat_add(part, io_ticks, 1); + __part_stat_add(part, io_ticks, end ? now - stamp : 1); } } if (part->partno) { @@ -1785,7 +1785,7 @@ void generic_start_io_acct(struct request_queue *q, int op, part_stat_lock(); - update_io_ticks(part, jiffies); + update_io_ticks(part, jiffies, false); part_stat_inc(part, ios[sgrp]); part_stat_add(part, sectors[sgrp], sectors); part_inc_in_flight(q, part, op_is_write(op)); @@ -1803,7 +1803,7 @@ void generic_end_io_acct(struct request_queue *q, int req_op, part_stat_lock(); - update_io_ticks(part, now); + update_io_ticks(part, now, true); part_stat_add(part, nsecs[sgrp], jiffies_to_nsecs(duration)); part_stat_add(part, time_in_queue, duration); part_dec_in_flight(q, part, op_is_write(req_op)); diff --git a/block/blk-core.c b/block/blk-core.c index abfdcf81a228..4401b30a1751 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1337,7 +1337,7 @@ void blk_account_io_done(struct request *req, u64 now) part_stat_lock(); part = req->part; - update_io_ticks(part, jiffies); + update_io_ticks(part, jiffies, true); part_stat_inc(part, ios[sgrp]); part_stat_add(part, nsecs[sgrp], now - req->start_time_ns); part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns)); @@ -1379,7 +1379,7 @@ void blk_account_io_start(struct request *rq, bool new_io) rq->part = part; } - update_io_ticks(part, jiffies); + update_io_ticks(part, jiffies, false); part_stat_unlock(); } diff --git a/include/linux/genhd.h b/include/linux/genhd.h index d5c75df64bba..f1066f10b062 100644 --- a/include/linux/genhd.h +++ b/include/linux/genhd.h @@ -467,7 +467,7 @@ static inline void free_part_info(struct hd_struct *part) kfree(part->info); } -void update_io_ticks(struct hd_struct *part, unsigned long now); +void update_io_ticks(struct hd_struct *part, unsigned long now, bool end); /* block/genhd.c */ extern void device_add_disk(struct device *parent, struct gendisk *disk,