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 A90A0C001B0 for ; Sun, 23 Jul 2023 10:50:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229891AbjGWKuj (ORCPT ); Sun, 23 Jul 2023 06:50:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60672 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229862AbjGWKui (ORCPT ); Sun, 23 Jul 2023 06:50:38 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DDE8AE64; Sun, 23 Jul 2023 03:50:34 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 6D1F460BFF; Sun, 23 Jul 2023 10:50:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 750E7C433CA; Sun, 23 Jul 2023 10:50:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1690109433; bh=rpf1pzEGimfS+pD7lRpXpbhbCeda9Jos1hrb2yJB+3o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=AgDxLM3+DwaT9S0gw6BQrgBgnyNIKBC/96qyekEg37ek2YIII/yUKhNVehnNayAkw iGkanKS4hAJRD7NHnXSxf+6P18dlJy+xDjbVhEXKYmA0PwiYnVN7cyhMZCNHyq8Vq0 dqkXmgTF2tqJarZJLppEQJTJbkRkWgakaUSI4Wis= Date: Sun, 23 Jul 2023 12:50:30 +0200 From: Greg Kroah-Hartman To: Oleksandr Natalenko Cc: stable@vger.kernel.org, Pavel Begunkov , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, Andres Freund , Jens Axboe Subject: Re: [PATCH 6.4 800/800] io_uring: Use io_schedule* in cqring wait Message-ID: <2023072310-superman-frosted-7321@gregkh> References: <20230716194949.099592437@linuxfoundation.org> <20230716195007.731909670@linuxfoundation.org> <12251678.O9o76ZdvQC@natalenko.name> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <12251678.O9o76ZdvQC@natalenko.name> Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Sun, Jul 23, 2023 at 11:39:42AM +0200, Oleksandr Natalenko wrote: > Hello. > > On neděle 16. července 2023 21:50:53 CEST Greg Kroah-Hartman wrote: > > From: Andres Freund > > > > commit 8a796565cec3601071cbbd27d6304e202019d014 upstream. > > > > I observed poor performance of io_uring compared to synchronous IO. That > > turns out to be caused by deeper CPU idle states entered with io_uring, > > due to io_uring using plain schedule(), whereas synchronous IO uses > > io_schedule(). > > > > The losses due to this are substantial. On my cascade lake workstation, > > t/io_uring from the fio repository e.g. yields regressions between 20% > > and 40% with the following command: > > ./t/io_uring -r 5 -X0 -d 1 -s 1 -c 1 -p 0 -S$use_sync -R 0 /mnt/t2/fio/write.0.0 > > > > This is repeatable with different filesystems, using raw block devices > > and using different block devices. > > > > Use io_schedule_prepare() / io_schedule_finish() in > > io_cqring_wait_schedule() to address the difference. > > > > After that using io_uring is on par or surpassing synchronous IO (using > > registered files etc makes it reliably win, but arguably is a less fair > > comparison). > > > > There are other calls to schedule() in io_uring/, but none immediately > > jump out to be similarly situated, so I did not touch them. Similarly, > > it's possible that mutex_lock_io() should be used, but it's not clear if > > there are cases where that matters. > > > > Cc: stable@vger.kernel.org # 5.10+ > > Cc: Pavel Begunkov > > Cc: io-uring@vger.kernel.org > > Cc: linux-kernel@vger.kernel.org > > Signed-off-by: Andres Freund > > Link: https://lore.kernel.org/r/20230707162007.194068-1-andres@anarazel.de > > [axboe: minor style fixup] > > Signed-off-by: Jens Axboe > > Signed-off-by: Greg Kroah-Hartman > > --- > > io_uring/io_uring.c | 15 +++++++++++++-- > > 1 file changed, 13 insertions(+), 2 deletions(-) > > > > --- a/io_uring/io_uring.c > > +++ b/io_uring/io_uring.c > > @@ -2575,6 +2575,8 @@ int io_run_task_work_sig(struct io_ring_ > > static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx, > > struct io_wait_queue *iowq) > > { > > + int token, ret; > > + > > if (unlikely(READ_ONCE(ctx->check_cq))) > > return 1; > > if (unlikely(!llist_empty(&ctx->work_llist))) > > @@ -2585,11 +2587,20 @@ static inline int io_cqring_wait_schedul > > return -EINTR; > > if (unlikely(io_should_wake(iowq))) > > return 0; > > + > > + /* > > + * Use io_schedule_prepare/finish, so cpufreq can take into account > > + * that the task is waiting for IO - turns out to be important for low > > + * QD IO. > > + */ > > + token = io_schedule_prepare(); > > + ret = 0; > > if (iowq->timeout == KTIME_MAX) > > schedule(); > > else if (!schedule_hrtimeout(&iowq->timeout, HRTIMER_MODE_ABS)) > > - return -ETIME; > > - return 0; > > + ret = -ETIME; > > + io_schedule_finish(token); > > + return ret; > > } > > > > /* > > Reportedly, this caused a regression as reported in [1] [2] [3]. Not only v6.4.4 is affected, v6.1.39 is affected too. > > Reverting this commit fixes the issue. > > Please check. Is this also an issue in 6.5-rc2? thanks, greg k-h