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 270F2C77B6D for ; Mon, 3 Apr 2023 09:23:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231679AbjDCJXu (ORCPT ); Mon, 3 Apr 2023 05:23:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50588 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231962AbjDCJXo (ORCPT ); Mon, 3 Apr 2023 05:23:44 -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 15622EC4C for ; Mon, 3 Apr 2023 02:22:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1680513746; 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=LxZ9/V62aRV4MHBcdF0RXnCsBbp2tO2Tl22tusojnlg=; b=WLW9VAz8/FMQDiG2Y8jzDcBSxtgDWDKu8W5n8nPHi9YMvkFqkF8UGbfiD6xRz4BlVwW6hV Y+g+Q97GlC56pJNIEdnAPRb4o7w4wPhUH4AicMGnDZrNMsJ0jTx4nGAGLNE98SWsEzI5PJ gOMTcnHOKLeXANKZ2zs5ogN+CwmVKRA= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-184-YCBs7t7aN5Ckf_chgGq9rg-1; Mon, 03 Apr 2023 05:22:22 -0400 X-MC-Unique: YCBs7t7aN5Ckf_chgGq9rg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 90922185A794; Mon, 3 Apr 2023 09:22:21 +0000 (UTC) Received: from ovpn-8-18.pek2.redhat.com (ovpn-8-20.pek2.redhat.com [10.72.8.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8AA9840C20FA; Mon, 3 Apr 2023 09:22:14 +0000 (UTC) Date: Mon, 3 Apr 2023 17:22:09 +0800 From: Ming Lei To: Ziyang Zhang Cc: linux-kernel@vger.kernel.org, Miklos Szeredi , Xiaoguang Wang , Bernd Schubert , Pavel Begunkov , io-uring@vger.kernel.org, Stefan Hajnoczi , linux-block@vger.kernel.org, Jens Axboe , Dan Williams , ming.lei@redhat.com Subject: Re: [PATCH V5 16/16] block: ublk_drv: apply io_uring FUSED_CMD for supporting zero copy Message-ID: References: <20230328150958.1253547-1-ming.lei@redhat.com> <20230328150958.1253547-17-ming.lei@redhat.com> <2e3c20e0-a0be-eaf3-b288-c3c8fa31d1fa@linux.alibaba.com> <08b047a8-c577-a717-81a8-db8fca8ebab6@linux.alibaba.com> <1d74e886-89af-bbbb-9bae-37d20ce07fb2@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1d74e886-89af-bbbb-9bae-37d20ce07fb2@linux.alibaba.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Apr 03, 2023 at 04:38:30PM +0800, Ziyang Zhang wrote: > On 2023/3/29 18:52, Ming Lei wrote: > > On Wed, Mar 29, 2023 at 06:01:16PM +0800, Ziyang Zhang wrote: > >> On 2023/3/29 17:00, Ming Lei wrote: > >>> On Wed, Mar 29, 2023 at 10:57:53AM +0800, Ziyang Zhang wrote: > >>>> On 2023/3/28 23:09, Ming Lei wrote: > >>>>> Apply io_uring fused command for supporting zero copy: > >>>>> > >>>> > >>>> [...] > >>>> > >>>>> > >>>>> @@ -1374,7 +1533,12 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags) > >>>>> if (!ubq || ub_cmd->q_id != ubq->q_id) > >>>>> goto out; > >>>>> > >>>>> - if (ubq->ubq_daemon && ubq->ubq_daemon != current) > >>>>> + /* > >>>>> + * The fused command reads the io buffer data structure only, so it > >>>>> + * is fine to be issued from other context. > >>>>> + */ > >>>>> + if ((ubq->ubq_daemon && ubq->ubq_daemon != current) && > >>>>> + (cmd_op != UBLK_IO_FUSED_SUBMIT_IO)) > >>>>> goto out; > >>>>> > >>>> > >>>> Hi Ming, > >>>> > >>>> What is your use case that fused io_uring cmd is issued from another thread? > >>>> I think it is good practice to operate one io_uring instance in one thread > >>>> only. > >>> > >>> So far we limit io command has to be issued from the queue context, > >>> which is still not friendly from userspace viewpoint, the reason is > >>> that we can't get io_uring exit notification and ublk's use case is > >>> very special since the queued io command may not be completed forever, > >> > >> OK, so UBLK_IO_FUSED_SUBMIT_IO is guaranteed to be completed because it is > >> not queued. FETCH_REQ and COMMIT_AMD_FETCH are queued io commands and could > >> not be completed forever so they have to be issued from ubq_daemon. Right? > > > > Yeah, any io command should be issued from ubq daemon context. > > > >> > >> BTW, maybe NEED_GET_DATA can be issued from other context... > > > > So far it won't be supported. > > > > As I mentioned in the link, if io_uring can provide io_uring exit > > callback, we may relax this limit. > > > > Hi, Ming > > Sorry, I do not understand... I think UBLK_IO_NEED_GET_DATA is normal IO just like > UBLK_IO_FUSED_SUBMIT_IO. It is issued from one pthread(ubq_daemon for now) and > is completed just in time(not queued). So I think we can allow UBLK_IO_NEED_GET_DATA > to be issued from other context. No, it isn't. UBLK_IO_FUSED_SUBMIT_IO is actually for handling target IO, and this command just reads/provides IO buffer meta to io_uring in read-only approach, and io buffer meta won't be changed, and any io state won't be changed, so it is fine to call concurrently. UBLK_IO_NEED_GET_DATA is still part of io commands, in which io->addr needs to be set, and io->flags is touched, and it can't be done safely concurrently. Also after zero-copy is supported, UBLK_IO_NEED_GET_DATA may become legacy code path, because ublk server can read/write io data directly in userspace via read()/write(), and there isn't buffer allocation issue any more. Thanks, Ming