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 1FDB8C6FD18 for ; Tue, 25 Apr 2023 14:43:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233943AbjDYOnW (ORCPT ); Tue, 25 Apr 2023 10:43:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54088 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234175AbjDYOnV (ORCPT ); Tue, 25 Apr 2023 10:43:21 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D88E11BF4 for ; Tue, 25 Apr 2023 07:42:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1682433752; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ahPqfnnmFpWSxXmgJdynz+bE7M52y4t/RO+O7Mj5zgo=; b=E9E+OwjAIojedsGnT60GQ1xpcoQPuIxhx6CaJzacwZ2EdfjZk1Omny+dflj+yWI51pQFeq 7K+UCy12X39dJWwRwv84F2feN9vtQJxMqxPdajGsxfmxowbpUEdFntejav3zqt/asEijg2 HhRg9ptnxr53hF7lfUYcYdS10xuwOtU= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-592-SRAUN97MMlK7in1bdFJR2w-1; Tue, 25 Apr 2023 10:42:29 -0400 X-MC-Unique: SRAUN97MMlK7in1bdFJR2w-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D3D941C05148; Tue, 25 Apr 2023 14:42:28 +0000 (UTC) Received: from ovpn-8-24.pek2.redhat.com (ovpn-8-24.pek2.redhat.com [10.72.8.24]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 462E92166B47; Tue, 25 Apr 2023 14:42:25 +0000 (UTC) Date: Tue, 25 Apr 2023 22:42:20 +0800 From: Ming Lei To: Jens Axboe Cc: io-uring@vger.kernel.org, ming.lei@redhat.com Subject: Re: [PATCH 4/4] io_uring: mark opcodes that always need io-wq punt Message-ID: References: <20230420183135.119618-1-axboe@kernel.dk> <20230420183135.119618-5-axboe@kernel.dk> <478df0f7-c167-76f3-3fd8-9d5771a44048@kernel.dk> <0e5910a9-d776-cdea-1852-edd995f93dc8@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0e5910a9-d776-cdea-1852-edd995f93dc8@kernel.dk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Tue, Apr 25, 2023 at 07:31:10AM -0600, Jens Axboe wrote: > On 4/24/23 8:50?PM, Ming Lei wrote: > > On Mon, Apr 24, 2023 at 08:18:02PM -0600, Jens Axboe wrote: > >> On 4/24/23 8:13?PM, Ming Lei wrote: > >>> On Mon, Apr 24, 2023 at 08:08:09PM -0600, Jens Axboe wrote: > >>>> On 4/24/23 6:57?PM, Ming Lei wrote: > >>>>> On Mon, Apr 24, 2023 at 09:24:33AM -0600, Jens Axboe wrote: > >>>>>> On 4/24/23 1:30?AM, Ming Lei wrote: > >>>>>>> On Thu, Apr 20, 2023 at 12:31:35PM -0600, Jens Axboe wrote: > >>>>>>>> Add an opdef bit for them, and set it for the opcodes where we always > >>>>>>>> need io-wq punt. With that done, exclude them from the file_can_poll() > >>>>>>>> check in terms of whether or not we need to punt them if any of the > >>>>>>>> NO_OFFLOAD flags are set. > >>>>>>>> > >>>>>>>> Signed-off-by: Jens Axboe > >>>>>>>> --- > >>>>>>>> io_uring/io_uring.c | 2 +- > >>>>>>>> io_uring/opdef.c | 22 ++++++++++++++++++++-- > >>>>>>>> io_uring/opdef.h | 2 ++ > >>>>>>>> 3 files changed, 23 insertions(+), 3 deletions(-) > >>>>>>>> > >>>>>>>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c > >>>>>>>> index fee3e461e149..420cfd35ebc6 100644 > >>>>>>>> --- a/io_uring/io_uring.c > >>>>>>>> +++ b/io_uring/io_uring.c > >>>>>>>> @@ -1948,7 +1948,7 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags) > >>>>>>>> return -EBADF; > >>>>>>>> > >>>>>>>> if (issue_flags & IO_URING_F_NO_OFFLOAD && > >>>>>>>> - (!req->file || !file_can_poll(req->file))) > >>>>>>>> + (!req->file || !file_can_poll(req->file) || def->always_iowq)) > >>>>>>>> issue_flags &= ~IO_URING_F_NONBLOCK; > >>>>>>> > >>>>>>> I guess the check should be !def->always_iowq? > >>>>>> > >>>>>> How so? Nobody that takes pollable files should/is setting > >>>>>> ->always_iowq. If we can poll the file, we should not force inline > >>>>>> submission. Basically the ones setting ->always_iowq always do -EAGAIN > >>>>>> returns if nonblock == true. > >>>>> > >>>>> I meant IO_URING_F_NONBLOCK is cleared here for ->always_iowq, and > >>>>> these OPs won't return -EAGAIN, then run in the current task context > >>>>> directly. > >>>> > >>>> Right, of IO_URING_F_NO_OFFLOAD is set, which is entirely the point of > >>>> it :-) > >>> > >>> But ->always_iowq isn't actually _always_ since fallocate/fsync/... are > >>> not punted to iowq in case of IO_URING_F_NO_OFFLOAD, looks the naming of > >>> ->always_iowq is a bit confusing? > >> > >> Yeah naming isn't that great, I can see how that's bit confusing. I'll > >> be happy to take suggestions on what would make it clearer. > > > > Except for the naming, I am also wondering why these ->always_iowq OPs > > aren't punted to iowq in case of IO_URING_F_NO_OFFLOAD, given it > > shouldn't improve performance by doing so because these OPs are supposed > > to be slow and always slept, not like others(buffered writes, ...), > > can you provide one hint about not offloading these OPs? Or is it just that > > NO_OFFLOAD needs to not offload every OPs? > > The whole point of NO_OFFLOAD is that items that would normally be > passed to io-wq are just run inline. This provides a way to reap the > benefits of batched submissions and syscall reductions. Some opcodes > will just never be async, and io-wq offloads are not very fast. Some of Yeah, seems io-wq is much slower than inline issue, maybe it needs to be looked into, and it is easy to run into io-wq for IOSQE_IO_LINK. > them can eventually be migrated to async support, if the underlying > mechanics support it. > > You'll note that none of the ->always_iowq opcodes are pollable. If True, then looks the ->always_iowq flag doesn't make a difference here because your patch clears IO_URING_F_NONBLOCK for !file_can_poll(req->file). Also almost all these ->always_iowq OPs are slow and blocked, if they are issued inline, the submission pipeline will be blocked. > NO_OFFLOAD is setup, it's pointless NOT to issue them with NONBLOCK > cleared, as you'd just get -EAGAIN and then need to call them again with > NONBLOCK cleared from the same context. My point is that these OPs are slow and slept, so inline issue won't improve performance actually for them, and punting to io-wq couldn't be worse too. On the other side, inline issue may hurt perf because submission pipeline is blocked when issuing these OPs. Thanks, Ming