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=-11.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 AC607C433E1 for ; Thu, 27 Aug 2020 08:47:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8F6452177B for ; Thu, 27 Aug 2020 08:47:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728015AbgH0IrD (ORCPT ); Thu, 27 Aug 2020 04:47:03 -0400 Received: from mx2.suse.de ([195.135.220.15]:33666 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726988AbgH0IrC (ORCPT ); Thu, 27 Aug 2020 04:47:02 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id CB82AAC7D; Thu, 27 Aug 2020 08:47:31 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 041D31E12C0; Thu, 27 Aug 2020 10:46:59 +0200 (CEST) Date: Thu, 27 Aug 2020 10:46:58 +0200 From: Jan Kara To: =?utf-8?B?55Sw?= Cc: Jan Kara , "bcrl@kvack.org" , "viro@zeniv.linux.org.uk" , "linux-aio@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] aio: use wait_for_completion_io() when waiting for completion of io Message-ID: <20200827084658.GC15885@quack2.suse.cz> References: <1596634551-27526-1-git-send-email-xianting_tian@126.com> <20200826132330.GD15126@quack2.suse.cz> <26ae9330.63f4.1742b70dd88.Coremail.xianting_tian@126.com> <20200827075537.GA15885@quack2.suse.cz> <5ef5b380.877b.1742f087437.Coremail.xianting_tian@126.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5ef5b380.877b.1742f087437.Coremail.xianting_tian@126.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi! On Thu 27-08-20 16:28:37, 田 wrote: > I understood what you said before:) Good :) > Totally agree with you, that we should fix the common path to make it to > account IO wait time. Currently kernel only has io_wait_event(), which > does not support timeout, maybe we need develop new interface like > io_wait_event_hrtimeout(), then we can use it instead of > wait_event_interruptible_hrtimeout()? Yes, that's what I'd do. Honza > > On 08/27/2020 15:55, Jan Kara wrote: > Hello! > > On Wed 26-08-20 23:44:11, 田 wrote: > > thanks for your kindly reply, > > the normal wait path read_events()->wait_event_interruptible_hrtimeout(), > > which will call schedule(), it does not account IO wait time. > > Not sure if there isn't some misunderstanding so I'll repeat what I've > said: Yes, above path will not account as IO wait time and IMO that is much > more common path which should be accounted as IO wait time. So I think that > without fixing that path, fixing cornercases like you did in your patch is > rather pointless. > > Honza > > > On 08/26/2020 21:23, Jan Kara wrote: > > On Wed 05-08-20 09:35:51, Xianting Tian wrote: > > > When waiting for the completion of io, we need account iowait time. As > > > wait_for_completion() calls schedule_timeout(), which doesn't account > > > iowait time. While wait_for_completion_io() calls io_schedule_timeout(), > > > which will account iowait time. > > > > > > So using wait_for_completion_io() instead of wait_for_completion() > > > when waiting for completion of io before exit_aio and io_destroy. > > > > > > Signed-off-by: Xianting Tian > > > > Thanks for the patch! It looks good to me but IMO this is just scratching > > the surface. E.g. for AIO we are mostly going to wait in read_events() by > > wait_event_interruptible_hrtimeout() and *that* doesn't account as IO wait > > either? Which is IMO far bigger misaccounting... The two case you fix seem > > to be just rare cornercases so what they do isn't a big deal either way. > > > > So I agree it may be worth it to properly account waiting for AIO but if > > you want to do that, then please handle mainly the common cases in AIO > > code. > > > > Honza > > > > > --- > > > fs/aio.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/fs/aio.c b/fs/aio.c > > > index 91e7cc4..498b8a0 100644 > > > --- a/fs/aio.c > > > +++ b/fs/aio.c > > > @@ -892,7 +892,7 @@ void exit_aio(struct mm_struct *mm) > > > > > > if (!atomic_sub_and_test(skipped, &wait.count)) { > > > /* Wait until all IO for the context are done. */ > > > - wait_for_completion(&wait.comp); > > > + wait_for_completion_io(&wait.comp); > > > } > > > > > > RCU_INIT_POINTER(mm->ioctx_table, NULL); > > > @@ -1400,7 +1400,7 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr, > > > * is destroyed. > > > */ > > > if (!ret) > > > - wait_for_completion(&wait.comp); > > > + wait_for_completion_io(&wait.comp); > > > > > > return ret; > > > } > > > -- > > > 1.8.3.1 > > > > > -- > > Jan Kara > > SUSE Labs, CR > -- > Jan Kara > SUSE Labs, CR -- Jan Kara SUSE Labs, CR