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.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 208BFC77B75 for ; Tue, 9 May 2023 19:08:03 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.532462.828698 (Exim 4.92) (envelope-from ) id 1pwSgY-000892-4L; Tue, 09 May 2023 19:07:42 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 532462.828698; Tue, 09 May 2023 19:07:42 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1pwSgY-00088v-1R; Tue, 09 May 2023 19:07:42 +0000 Received: by outflank-mailman (input) for mailman id 532462; Tue, 09 May 2023 19:07:40 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1pwSgW-00088p-Ci for xen-devel@lists.xenproject.org; Tue, 09 May 2023 19:07:40 +0000 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id c2a87f95-ee9c-11ed-8611-37d641c3527e; Tue, 09 May 2023 21:07:37 +0200 (CEST) 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-529-B9dAK25vNzSSerVDhtPZ3A-1; Tue, 09 May 2023 15:07:32 -0400 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 6C0DE872011; Tue, 9 May 2023 19:07:30 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.192]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C565640C6E67; Tue, 9 May 2023 19:07:24 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: c2a87f95-ee9c-11ed-8611-37d641c3527e DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683659256; 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=3tJ3xOkIIK9sjNiEc9UslJdWtKHgMpCwgj/6/bqEnvw=; b=dO7BhPExgWVSedrdEDDS0Yo9SP/3abgm/piFKl4HpwT7OswgDHiGJYIMhFkUVHYncWwMrb MG6vzm6KFRzt2HAOtkx8KUE5NGszaXCmwn15PpUXphNJfDgWCTz4RnaIeIbPgOLTmBHnL5 bYYSGP5vlc6TwCnFl6EYmJwsWeToMUM= X-MC-Unique: B9dAK25vNzSSerVDhtPZ3A-1 Date: Tue, 9 May 2023 21:07:23 +0200 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, Ronnie Sahlberg , Aarushi Mehta , qemu-block@nongnu.org, Paul Durrant , Anthony Perard , Peter Lieven , Stefan Weil , Xie Yongji , Paolo Bonzini , "Michael S. Tsirkin" , Leonardo Bras , Peter Xu , Hanna Reitz , Stefano Stabellini , Richard Henderson , David Woodhouse , Coiby Xu , Eduardo Habkost , Stefano Garzarella , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Julia Suvorova , xen-devel@lists.xenproject.org, eesposit@redhat.com, Juan Quintela , "Richard W.M. Jones" , Fam Zheng , Marcel Apfelbaum Subject: Re: [PATCH v5 00/21] block: remove aio_disable_external() API Message-ID: References: <20230504195327.695107-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230504195327.695107-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Am 04.05.2023 um 21:53 hat Stefan Hajnoczi geschrieben: > v5: > - Use atomic accesses for in_flight counter in vhost-user-server.c [Kevin] > - Stash SCSIDevice id/lun values for VIRTIO_SCSI_T_TRANSPORT_RESET event > before unrealizing the SCSIDevice [Kevin] > - Keep vhost-user-blk export .detach() callback so ctx is set to NULL [Kevin] > - Narrow BdrvChildClass and BlockDriver drained_{begin/end/poll} callbacks from > IO_OR_GS_CODE() to GLOBAL_STATE_CODE() [Kevin] > - Include Kevin's "block: Fix use after free in blockdev_mark_auto_del()" to > fix a latent bug that was exposed by this series > > v4: > - Remove external_disable_cnt variable [Philippe] > - Add Patch 1 to fix assertion failure in .drained_end() -> blk_get_aio_context() > v3: > - Resend full patch series. v2 was sent in the middle of a git rebase and was > missing patches. [Eric] > - Apply Reviewed-by tags. > v2: > - Do not rely on BlockBackend request queuing, implement .drained_begin/end() > instead in xen-block, virtio-blk, and virtio-scsi [Paolo] > - Add qdev_is_realized() API [Philippe] > - Add patch to avoid AioContext lock around blk_exp_ref/unref() [Paolo] > - Add patch to call .drained_begin/end() from main loop thread to simplify > callback implementations > > The aio_disable_external() API temporarily suspends file descriptor monitoring > in the event loop. The block layer uses this to prevent new I/O requests being > submitted from the guest and elsewhere between bdrv_drained_begin() and > bdrv_drained_end(). > > While the block layer still needs to prevent new I/O requests in drained > sections, the aio_disable_external() API can be replaced with > .drained_begin/end/poll() callbacks that have been added to BdrvChildClass and > BlockDevOps. > > This newer .bdrained_begin/end/poll() approach is attractive because it works > without specifying a specific AioContext. The block layer is moving towards > multi-queue and that means multiple AioContexts may be processing I/O > simultaneously. > > The aio_disable_external() was always somewhat hacky. It suspends all file > descriptors that were registered with is_external=true, even if they have > nothing to do with the BlockDriverState graph nodes that are being drained. > It's better to solve a block layer problem in the block layer than to have an > odd event loop API solution. > > The approach in this patch series is to implement BlockDevOps > .drained_begin/end() callbacks that temporarily stop file descriptor handlers. > This ensures that new I/O requests are not submitted in drained sections. Patches 2-16: Reviewed-by: Kevin Wolf