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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E0ABC433EF for ; Mon, 25 Apr 2022 15:37:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242884AbiDYPkP (ORCPT ); Mon, 25 Apr 2022 11:40:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48262 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239039AbiDYPkM (ORCPT ); Mon, 25 Apr 2022 11:40:12 -0400 Received: from ale.deltatee.com (ale.deltatee.com [204.191.154.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE5FE1C118; Mon, 25 Apr 2022 08:37:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=deltatee.com; s=20200525; h=Subject:In-Reply-To:From:References:Cc:To: MIME-Version:Date:Message-ID:content-disposition; bh=WSBP0lL4ZxsD/S52QMFKfvBtMxzOVM8DW0FzyMIL2N0=; b=ZPT8mymtViz6khblRWZPsoAZ+S fhl9v5tQMg2oGPBmwHYwb6DMdkGEUop1DTvDlWqi/gcFT/LPsRehwEQqAa7SfhL323lqGqfzdwu3B eAEG5qVNNoqVe2XtCeAUE0tX7FWIdqoj0ZsGk6EYDJLzCX7WxOb9oyAjWSGxypylFtrIW1JL7bzQG 5lJCdXPr5zSzcbYjvjdRf0LUA5ed2ELD9qJ53KaFzFr4LU4B4wOOcn9R4qBmQii48tn/YDMLuX1y6 W1mLjctHrX82SxLkw5hPcVrxWC5TPqvmCUbtp9JZ93gLDf2JJQlyWxThkmOLP63bAmRGK2fac89a/ BGAjLgLQ==; Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94.2) (envelope-from ) id 1nj0lr-00GHEE-H9; Mon, 25 Apr 2022 09:37:04 -0600 Message-ID: <7d69497a-cd2a-bf4e-c185-ebdba70e9937@deltatee.com> Date: Mon, 25 Apr 2022 09:37:00 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Content-Language: en-CA To: Guoqing Jiang , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, Song Liu Cc: Christoph Hellwig , Stephen Bates , Martin Oliveira , David Sloan References: <20220420195425.34911-1-logang@deltatee.com> <243b3e7f-1fa1-700c-a850-caaf45d95cde@linux.dev> From: Logan Gunthorpe In-Reply-To: <243b3e7f-1fa1-700c-a850-caaf45d95cde@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: guoqing.jiang@linux.dev, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, song@kernel.org, hch@infradead.org, sbates@raithlin.com, Martin.Oliveira@eideticom.com, David.Sloan@eideticom.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v2 00/12] Improve Raid5 Lock Contention X-SA-Exim-Version: 4.2.1 (built Sat, 13 Feb 2021 17:57:42 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022-04-24 01:53, Guoqing Jiang wrote: > > > On 4/21/22 3:54 AM, Logan Gunthorpe wrote: >> Hi, >> >> This is v2 of this series which addresses Christoph's feedback and >> fixes some bugs. The first posting is at [1]. A git branch is >> available at [2]. >> >> -- >> >> I've been doing some work trying to improve the bulk write performance >> of raid5 on large systems with fast NVMe drives. The bottleneck appears >> largely to be lock contention on the hash_lock and device_lock. This >> series improves the situation slightly by addressing a couple of low >> hanging fruit ways to take the lock fewer times in the request path. >> >> Patch 9 adjusts how batching works by keeping a reference to the >> previous stripe_head in raid5_make_request(). Under most situtations, >> this removes the need to take the hash_lock in stripe_add_to_batch_list() >> which should reduce the number of times the lock is taken by a factor of >> about 2. >> >> Patch 12 pivots the way raid5_make_request() works. Before the patch, the >> code must find the stripe_head for every 4KB page in the request, so each >> stripe head must be found once for every data disk. The patch changes this >> so that all the data disks can be added to a stripe_head at once and the >> number of times the stripe_head must be found (and thus the number of >> times the hash_lock is taken) should be reduced by a factor roughly equal >> to the number of data disks. >> >> The remaining patches are just cleanup and prep patches for those two >> patches. >> >> Doing apples to apples testing this series on a small VM with 5 ram >> disks, I saw a bandwidth increase of roughly 14% and lock contentions >> on the hash_lock (as reported by lock stat) reduced by more than a factor >> of 5 (though it is still significantly contended). >> >> Testing on larger systems with NVMe drives saw similar small bandwidth >> increases from 3% to 20% depending on the parameters. Oddly small arrays >> had larger gains, likely due to them having lower starting bandwidths; I >> would have expected larger gains with larger arrays (seeing there >> should have been even fewer locks taken in raid5_make_request()). >> >> Logan >> >> [1] https://lkml.kernel.org/r/20220407164511.8472-1-logang@deltatee.com >> [2] https://github.com/sbates130272/linux-p2pmem raid5_lock_cont_v2 >> >> -- >> >> Changes since v1: >> - Rebased on current md-next branch (190a901246c69d79) >> - Added patch to create a helper for checking if a sector >> is ahead of the reshape (per Christoph) >> - Reworked the __find_stripe() patch to create a find_get_stripe() >> helper (per Christoph) >> - Added more patches to further refactor raid5_make_request() and >> pull most of the loop body into a helper function (per Christoph) >> - A few other minor cleanups (boolean return, droping casting when >> printing sectors, commit message grammar) as suggested by Christoph. >> - Fixed two uncommon but bad data corruption bugs in that were found. >> >> -- >> >> Logan Gunthorpe (12): >> md/raid5: Factor out ahead_of_reshape() function >> md/raid5: Refactor raid5_make_request loop >> md/raid5: Move stripe_add_to_batch_list() call out of add_stripe_bio() >> md/raid5: Move common stripe count increment code into __find_stripe() >> md/raid5: Factor out helper from raid5_make_request() loop >> md/raid5: Drop the do_prepare flag in raid5_make_request() >> md/raid5: Move read_seqcount_begin() into make_stripe_request() >> md/raid5: Refactor for loop in raid5_make_request() into while loop >> md/raid5: Keep a reference to last stripe_head for batch >> md/raid5: Refactor add_stripe_bio() >> md/raid5: Check all disks in a stripe_head for reshape progress >> md/raid5: Pivot raid5_make_request() > > Generally, I don't object the cleanup patches since the code looks more > cleaner. > But my concern is that since some additional function calls are added to > hot path > (raid5_make_request), could the performance be affected? There's a bit of logic added to the raid5_make_requests but it is all local and should be fast, and it reduces the amount of calls to the slow contended locks. > And I think patch 9 and patch 12 are helpful for performance > improvement,  did > you measure the performance without those cleanup patches? Yes, I compared performance with and without this entire series. Logan