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=-7.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 D089CC433E1 for ; Sun, 24 May 2020 10:00:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AFD5F2076C for ; Sun, 24 May 2020 10:00:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=movency.com header.i=@movency.com header.b="CJyLgB48" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728942AbgEXKAi (ORCPT ); Sun, 24 May 2020 06:00:38 -0400 Received: from mail.movency.com ([151.236.222.166]:48932 "EHLO b-6.movency.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728704AbgEXKAi (ORCPT ); Sun, 24 May 2020 06:00:38 -0400 X-Greylist: delayed 862 seconds by postgrey-1.27 at vger.kernel.org; Sun, 24 May 2020 06:00:36 EDT Received: by b-6.movency.com with ESMTPSA id 04O9kAQW1722314; Sun, 24 May 2020 09:46:10 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=movency.com; s=mail; t=1590313570; bh=7BbKC33g6/SJX0HzjCZQwGRQaPz1+PXkt/MsPwq9E8w=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=CJyLgB48NcEl+KvLnGv3WibuDbym811oaMyjEZ1ZO0MCYcDUELobQgrckBj+HTaU1 Mtpqgs5GhlHt6H7JbvylLaJwcvzuHBzwr4aP5P6+OwgIURhZl/i3XK5uo2W3NHrSgk IGtMTKO3O0a6mhRPxmMOIIv04OHQOKa8mwtPdiQQBgVGSCXbq8wE+C275GW/KDC8RZ NR5rJ/Dx2LYz9p42yoRkWLus5JkunLcR1QKgU7qJSLe/P2pnorYqlapIcXFuiqnCar uTuQZbQX8V7c2WT/RR2+bGnUAYNyG71HtK5p5M/RZlvn309aJxUPszKex29bTU+xvg 8RDjBmlrtL6ZA== Subject: Re: [PATCHSET v2 0/12] Add support for async buffered reads To: Jens Axboe , io-uring@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20200523185755.8494-1-axboe@kernel.dk> <2b42c0c3-5d3c-e381-4193-83cb3f971399@kernel.dk> From: Chris Panayis Message-ID: <43ee202c-ffd1-2276-3c8d-7d5201b60684@movency.com> Date: Sun, 24 May 2020 10:46:10 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <2b42c0c3-5d3c-e381-4193-83cb3f971399@kernel.dk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-GB Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Yes! Jens & Team! Yes! My code has never looked so beautiful, been so efficient and run so well since switching to io_uring/async awesome-ness.. Really, really is a game-changer in terms of software design, control, performance, expressiveness... so many levels. Really, really great work! Thank you! Chris On 23/05/2020 20:20, Jens Axboe wrote: > And this one is v3, obviously, not v2... > > > On 5/23/20 12:57 PM, Jens Axboe wrote: >> We technically support this already through io_uring, but it's >> implemented with a thread backend to support cases where we would >> block. This isn't ideal. >> >> After a few prep patches, the core of this patchset is adding support >> for async callbacks on page unlock. With this primitive, we can simply >> retry the IO operation. With io_uring, this works a lot like poll based >> retry for files that support it. If a page is currently locked and >> needed, -EIOCBQUEUED is returned with a callback armed. The callers >> callback is responsible for restarting the operation. >> >> With this callback primitive, we can add support for >> generic_file_buffered_read(), which is what most file systems end up >> using for buffered reads. XFS/ext4/btrfs/bdev is wired up, but probably >> trivial to add more. >> >> The file flags support for this by setting FMODE_BUF_RASYNC, similar >> to what we do for FMODE_NOWAIT. Open to suggestions here if this is >> the preferred method or not. >> >> In terms of results, I wrote a small test app that randomly reads 4G >> of data in 4K chunks from a file hosted by ext4. The app uses a queue >> depth of 32. If you want to test yourself, you can just use buffered=1 >> with ioengine=io_uring with fio. No application changes are needed to >> use the more optimized buffered async read. >> >> preadv for comparison: >> real 1m13.821s >> user 0m0.558s >> sys 0m11.125s >> CPU ~13% >> >> Mainline: >> real 0m12.054s >> user 0m0.111s >> sys 0m5.659s >> CPU ~32% + ~50% == ~82% >> >> This patchset: >> real 0m9.283s >> user 0m0.147s >> sys 0m4.619s >> CPU ~52% >> >> The CPU numbers are just a rough estimate. For the mainline io_uring >> run, this includes the app itself and all the threads doing IO on its >> behalf (32% for the app, ~1.6% per worker and 32 of them). Context >> switch rate is much smaller with the patchset, since we only have the >> one task performing IO. >> >> The goal here is efficiency. Async thread offload adds latency, and >> it also adds noticable overhead on items such as adding pages to the >> page cache. By allowing proper async buffered read support, we don't >> have X threads hammering on the same inode page cache, we have just >> the single app actually doing IO. >> >> Been beating on this and it's solid for me, and I'm now pretty happy >> with how it all turned out. Not aware of any missing bits/pieces or >> code cleanups that need doing. >> >> Series can also be found here: >> >> https://git.kernel.dk/cgit/linux-block/log/?h=async-buffered.3 >> >> or pull from: >> >> git://git.kernel.dk/linux-block async-buffered.3 >> >> fs/block_dev.c | 2 +- >> fs/btrfs/file.c | 2 +- >> fs/ext4/file.c | 2 +- >> fs/io_uring.c | 99 ++++++++++++++++++++++++++++++++++ >> fs/xfs/xfs_file.c | 2 +- >> include/linux/blk_types.h | 3 +- >> include/linux/fs.h | 5 ++ >> include/linux/pagemap.h | 64 ++++++++++++++++++++++ >> mm/filemap.c | 111 ++++++++++++++++++++++++-------------- >> 9 files changed, 245 insertions(+), 45 deletions(-) >> >> Changes since v2: >> - Get rid of unnecessary wait_page_async struct, just use wait_page_async >> - Add another prep handler, adding wake_page_match() >> - Use wake_page_match() in both callers >> Changes since v1: >> - Fix an issue with inline page locking >> - Fix a potential race with __wait_on_page_locked_async() >> - Fix a hang related to not setting page_match, thus missing a wakeup >> >