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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9ED2DC4332F for ; Thu, 10 Nov 2022 12:05:21 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ot6IY-0002HP-MY; Thu, 10 Nov 2022 07:04:46 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ot6IC-0002Gk-7n for qemu-devel@nongnu.org; Thu, 10 Nov 2022 07:04:28 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ot6I7-0004xe-1v for qemu-devel@nongnu.org; Thu, 10 Nov 2022 07:04:23 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668081857; 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=h7LDJGgH+YxPFQxg2v6qobEvt+nM4w57fzUEAAlfxAo=; b=NdgCrDqTpkudGmL38m0D0SVgz6BvdzFbNIac+w9Ol6rqPQNIwckIwlDqcEf2kjnrPtYmYB RCrRN+vFJlvtkXDBxrUB8tI7HXZRMUzSWk6cKxAJFfHB56+ZAyuMc78iJjdrATfwGQ/VKB ZXibmd7HRKmMY0XE7HJ4jCEZltrnrHk= 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-101-Eteapp4nOf6j2XU80ijcvA-1; Thu, 10 Nov 2022 07:04:13 -0500 X-MC-Unique: Eteapp4nOf6j2XU80ijcvA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CB003886461; Thu, 10 Nov 2022 12:04:12 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.15]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 92E2340C94AA; Thu, 10 Nov 2022 12:04:11 +0000 (UTC) Date: Thu, 10 Nov 2022 13:04:10 +0100 From: Kevin Wolf To: Hanna Reitz Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, John Snow , Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH for-7.2 1/5] block/mirror: Do not wait for active writes Message-ID: References: <20221109165452.67927-1-hreitz@redhat.com> <20221109165452.67927-2-hreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221109165452.67927-2-hreitz@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, T_SPF_TEMPERROR=0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 09.11.2022 um 17:54 hat Hanna Reitz geschrieben: > Waiting for all active writes to settle before daring to create a > background copying operation means that we will never do background > operations while the guest does anything (in write-blocking mode), and > therefore cannot converge. Yes, we also will not diverge, but actually > converging would be even nicer. > > It is unclear why we did decide to wait for all active writes to settle > before creating a background operation, but it just does not seem > necessary. Active writes will put themselves into the in_flight bitmap > and thus properly block actually conflicting background requests. > > It is important for active requests to wait on overlapping background > requests, which we do in active_write_prepare(). However, so far it was > not documented why it is important. Add such documentation now, and > also to the other call of mirror_wait_on_conflicts(), so that it becomes > more clear why and when requests need to actively wait for other > requests to settle. > > Another thing to note is that of course we need to ensure that there are > no active requests when the job completes, but that is done by virtue of > the BDS being drained anyway, so there cannot be any active requests at > that point. > > With this change, we will need to explicitly keep track of how many > bytes are in flight in active requests so that > job_progress_set_remaining() in mirror_run() can set the correct number > of remaining bytes. > > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2123297 > Signed-off-by: Hanna Reitz Reviewed-by: Kevin Wolf > @@ -1327,6 +1336,7 @@ do_sync_target_write(MirrorBlockJob *job, MirrorMethod method, > abort(); > } > > + job->active_write_bytes_in_flight -= bytes; > if (ret >= 0) { > job_progress_update(&job->common.job, bytes); > } else { Preexisting, but it happens to be in the context: Don't we need to call job_progress_update() unconditionally? Otherwise, the total length will go backwards in the case of an error. Kevin