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 DF8C0C4332F for ; Tue, 7 Nov 2023 03:02:15 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1r0CLA-0008JK-Tz; Mon, 06 Nov 2023 22:01:20 -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 1r0CL6-0008Ir-Bx for qemu-devel@nongnu.org; Mon, 06 Nov 2023 22:01:17 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r0CL0-0008KM-Rj for qemu-devel@nongnu.org; Mon, 06 Nov 2023 22:01:16 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1699326068; 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=wp9waDfmpygdSjrcvQxLx4oS/EiJf0V6kYDI//fZRzY=; b=BB8JWhWkDVw/ddLqJgG+hmMMUVa7UsGHyVNBOcfCL1NV6xASfAG9dKeP9+J0dfsRNwnDXl ZIbEgnjP3CVJ4rd4Nv+ZtEfqHrlhSaf5NDjDfivuyDWO/hH0pU4/zJ9fiaR3OuTPykGxIC buQM2xGRXvPSM4DfmJLyk83pd2Xa+uw= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-588-1Qzp0PvKNb-UxLk01wIWzg-1; Mon, 06 Nov 2023 22:01:04 -0500 X-MC-Unique: 1Qzp0PvKNb-UxLk01wIWzg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E706C85A59D; Tue, 7 Nov 2023 03:01:03 +0000 (UTC) Received: from localhost (unknown [10.39.192.48]) by smtp.corp.redhat.com (Postfix) with ESMTP id E81E72166B26; Tue, 7 Nov 2023 03:01:02 +0000 (UTC) Date: Tue, 7 Nov 2023 11:00:49 +0800 From: Stefan Hajnoczi To: Kevin Wolf Cc: qemu-devel@nongnu.org, Markus Armbruster , Michal Privoznik , Paolo Bonzini , Eduardo Habkost , qemu-block@nongnu.org, Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Eric Blake , "Michael S. Tsirkin" , Hanna Reitz Subject: Re: [PATCH v2 0/2] virtio-blk: add iothread-vq-mapping parameter Message-ID: <20231107030049.GA949250@fedora> References: <20230918161604.1400051-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="pYgsa83QJm3plmjy" Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@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, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, T_SCC_BODY_TEXT_LINE=-0.01, 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 --pYgsa83QJm3plmjy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Nov 02, 2023 at 03:10:52PM +0100, Kevin Wolf wrote: > Am 18.09.2023 um 18:16 hat Stefan Hajnoczi geschrieben: > > virtio-blk and virtio-scsi devices need a way to specify the mapping be= tween > > IOThreads and virtqueues. At the moment all virtqueues are assigned to = a single > > IOThread or the main loop. This single thread can be a CPU bottleneck, = so it is > > necessary to allow finer-grained assignment to spread the load. With th= is > > series applied, "pidstat -t 1" shows that guests with -smp 2 or higher = are able > > to exploit multiple IOThreads. > >=20 > > This series introduces command-line syntax for the new iothread-vq-mapp= ing > > property is as follows: > >=20 > > --device '{"driver":"virtio-blk-pci","iothread-vq-mapping":[{"iothrea= d":"iothread0","vqs":[0,1,2]},...]},...' > >=20 > > IOThreads are specified by name and virtqueues are specified by 0-based > > index. > >=20 > > It will be common to simply assign virtqueues round-robin across a set > > of IOThreads. A convenient syntax that does not require specifying > > individual virtqueue indices is available: > >=20 > > --device '{"driver":"virtio-blk-pci","iothread-vq-mapping":[{"iothrea= d":"iothread0"},{"iothread":"iothread1"},...]},...' > >=20 > > There is no way to reassign virtqueues at runtime and I expect that to = be a > > very rare requirement. > >=20 > > Note that JSON --device syntax is required for the iothread-vq-mapping > > parameter because it's non-scalar. > >=20 > > Based-on: 20230912231037.826804-1-stefanha@redhat.com ("[PATCH v3 0/5] = block-backend: process I/O in the current AioContext") >=20 > Does this strictly depend on patch 5/5 of that series, or would it just > be a missed opportunity for optimisation by unnecessarily running some > requests from a different thread? "[PATCH v3 5/5] block-coroutine-wrapper: use qemu_get_current_aio_context()" is necessary so that virtio_blk_sect_range_ok -> blk_get_geometry -> blk_nb_sectors -> bdrv_refresh_total_sectors -> bdrv_poll_co can be called without holding the AioContext lock. That case only happens when the BlockDriverState is a file-posix host CD-ROM or a file-win32 host_device. Most users will never hit this problem, but it would be unsafe to proceed merging code without this patch. > I suspect it does depend on the other virtio-blk series, though: >=20 > [PATCH 0/4] virtio-blk: prepare for the multi-queue block layer > https://patchew.org/QEMU/20230914140101.1065008-1-stefanha@redhat.com/ >=20 > Is this right? Yes, it depends on "[PATCH 0/4] virtio-blk: prepare for the multi-queue block layer" so that every AioContext is able to handle Linux AIO or io_uring I/O and to stop using the AioContext lock in the virtio-blk I/O code path. Stefan >=20 > Given that soft freeze is early next week, maybe we should try to merge > just the bare minimum of strictly necessary dependencies. >=20 > Kevin >=20 --pYgsa83QJm3plmjy Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmVJqGEACgkQnKSrs4Gr c8gUcwf+IhJUqJKPFoLwvVHIDH3ZMNS31TglxVV+NYzguILwzd2vwobE8AYukePU GbnvYxYddI9IKeWYH27vfZ4L4R3LSvZdWcheKHRJTw3eWeez3aPckoanj2DZ6B7W 1fWGV7acdZd70DNYlfMgkFeRyTfgxhCqSwLwQbfYl3dffMzOsBXOFWhoGjhUBziz W41QJLCGyF7KyvGkcqxgJPFLf8x1MLUs1gghUvwFBpkjXOE9uUlwG98DvO69zCpP LxM4rtljykfrbflswdP+AUZ92mGvm2nkqASPhUoY+aE3SUovR6ULjHRGk2VoHhRq 715A3EYZ72o0NQvArqnoqC+4rLhY4A== =taeC -----END PGP SIGNATURE----- --pYgsa83QJm3plmjy--