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 X-Spam-Level: X-Spam-Status: No, score=-7.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2021DC64E7B for ; Tue, 1 Dec 2020 17:45:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ADC152151B for ; Tue, 1 Dec 2020 17:45:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="EqqwaJsp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389020AbgLARpR (ORCPT ); Tue, 1 Dec 2020 12:45:17 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:53115 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388004AbgLARpR (ORCPT ); Tue, 1 Dec 2020 12:45:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606844630; 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=knIDZSVvEYg05Fp1QEgiwa+zurWE4bXcDiX5a26vU3s=; b=EqqwaJsp9yeCIOxirdeoIgBMWRgsPvRFdEL8vnJ+Yw7XKdPmB5qK9vkR9uMRgm3Ceou4gh 7MKu0IgGP2d922X8QmWDPRzJe3S/FLWMESjaAe9LZSNWYrdgs8sCsWvBp+gup9AGzfWjaU Dtgd1/irlsFk95WdmdobU9OT9n8z5ZU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-258-KXv7Gs4cP82CK0P_xSKa6g-1; Tue, 01 Dec 2020 12:43:48 -0500 X-MC-Unique: KXv7Gs4cP82CK0P_xSKa6g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 425C61842164; Tue, 1 Dec 2020 17:43:46 +0000 (UTC) Received: from localhost (ovpn-114-82.ams2.redhat.com [10.36.114.82]) by smtp.corp.redhat.com (Postfix) with ESMTP id 58BDC5C1B4; Tue, 1 Dec 2020 17:43:39 +0000 (UTC) Date: Tue, 1 Dec 2020 17:43:38 +0000 From: Stefan Hajnoczi To: Stefano Garzarella Cc: "Michael S. Tsirkin" , Stefan Hajnoczi , Mike Christie , fam , linux-scsi , Jason Wang , qemu-devel , Linux Virtualization , target-devel , Paolo Bonzini Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq Message-ID: <20201201174338.GB595829@stefanha-x1.localdomain> References: <20201118113117.GF182763@stefanha-x1.localdomain> <20201119094315-mutt-send-email-mst@kernel.org> <20201120072802-mutt-send-email-mst@kernel.org> <20201201125943.GE585157@stefanha-x1.localdomain> <20201201134518.pwrggkmixpyro4sg@steredhat> MIME-Version: 1.0 In-Reply-To: <20201201134518.pwrggkmixpyro4sg@steredhat> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="/WwmFnJnmDyWGHa4" Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: target-devel@vger.kernel.org --/WwmFnJnmDyWGHa4 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Dec 01, 2020 at 02:45:18PM +0100, Stefano Garzarella wrote: > On Tue, Dec 01, 2020 at 12:59:43PM +0000, Stefan Hajnoczi wrote: > > On Fri, Nov 20, 2020 at 07:31:08AM -0500, Michael S. Tsirkin wrote: > > > On Fri, Nov 20, 2020 at 08:45:49AM +0000, Stefan Hajnoczi wrote: > > > > On Thu, Nov 19, 2020 at 5:08 PM Stefan Hajnoczi wrote: > > > > > > > > > > On Thu, Nov 19, 2020 at 4:43 PM Mike Christie > > > > > wrote: > > > > > > > > > > > > On 11/19/20 10:24 AM, Stefan Hajnoczi wrote: > > > > > > > On Thu, Nov 19, 2020 at 4:13 PM Mike Christie > > > > > > > wrote: > > > > > > >> > > > > > > >> On 11/19/20 8:46 AM, Michael S. Tsirkin wrote: > > > > > > >>> On Wed, Nov 18, 2020 at 11:31:17AM +0000, Stefan Hajnoczi w= rote: > > > > > > > struct vhost_run_worker_info { > > > > > > > struct timespec *timeout; > > > > > > > sigset_t *sigmask; > > > > > > > > > > > > > > /* List of virtqueues to process */ > > > > > > > unsigned nvqs; > > > > > > > unsigned vqs[]; > > > > > > > }; > > > > > > > > > > > > > > /* This blocks until the timeout is reached, a signal is rece= ived, or > > > > > > > the vhost device is destroyed */ > > > > > > > int ret =3D ioctl(vhost_fd, VHOST_RUN_WORKER, &info); > > > > > > > > > > > > > > As you can see, userspace isn't involved with dealing with th= e > > > > > > > requests. It just acts as a thread donor to the vhost driver. > > > > > > > > > > > > > > We would want the VHOST_RUN_WORKER calls to be infrequent to = avoid the > > > > > > > penalty of switching into the kernel, copying in the argument= s, etc. > > > > > > > > > > > > I didn't get this part. Why have the timeout? When the timeout = expires, > > > > > > does userspace just call right back down to the kernel or does = it do > > > > > > some sort of processing/operation? > > > > > > > > > > > > You could have your worker function run from that ioctl wait fo= r a > > > > > > signal or a wake up call from the vhost_work/poll functions. > > > > > > > > > > An optional timeout argument is common in blocking interfaces lik= e > > > > > poll(2), recvmmsg(2), etc. > > > > > > > > > > Although something can send a signal to the thread instead, > > > > > implementing that in an application is more awkward than passing = a > > > > > struct timespec. > > > > > > > > > > Compared to other blocking calls we don't expect > > > > > ioctl(VHOST_RUN_WORKER) to return soon, so maybe the timeout will > > > > > rarely be used and can be dropped from the interface. > > > > > > > > > > BTW the code I posted wasn't a carefully thought out proposal :).= The > > > > > details still need to be considered and I'm going to be offline f= or > > > > > the next week so maybe someone else can think it through in the > > > > > meantime. > > > > > > > > One final thought before I'm offline for a week. If > > > > ioctl(VHOST_RUN_WORKER) is specific to a single vhost device instan= ce > > > > then it's hard to support poll-mode (busy waiting) workers because > > > > each device instance consumes a whole CPU. If we stick to an interf= ace > > > > where the kernel manages the worker threads then it's easier to sha= re > > > > workers between devices for polling. > > >=20 > > >=20 > > > Yes that is the reason vhost did its own reason in the first place. > > >=20 > > >=20 > > > I am vaguely thinking about poll(2) or a similar interface, > > > which can wait for an event on multiple FDs. > >=20 > > I can imagine how using poll(2) would work from a userspace perspective= , > > but on the kernel side I don't think it can be implemented cleanly. > > poll(2) is tied to the file_operations->poll() callback and > > read/write/error events. Not to mention there isn't a way to substitue > > the vhost worker thread function instead of scheduling out the current > > thread while waiting for poll fd events. > >=20 > > But maybe ioctl(VHOST_WORKER_RUN) can do it: > >=20 > > struct vhost_run_worker_dev { > > int vhostfd; /* /dev/vhost-TYPE fd */ > > unsigned nvqs; /* number of virtqueues in vqs[] */ > > unsigned vqs[]; /* virtqueues to process */ > > }; > >=20 > > struct vhost_run_worker_info { > > struct timespec *timeout; > > sigset_t *sigmask; > >=20 > > unsigned ndevices; > > struct vhost_run_worker_dev *devices[]; > > }; > >=20 > > In the simple case userspace sets ndevices to 1 and we just handle > > virtqueues for the current device. > >=20 > > In the fancier shared worker thread case the userspace process has the > > vhost fds of all the devices it is processing and passes them to > > ioctl(VHOST_WORKER_RUN) via struct vhost_run_worker_dev elements. >=20 > Which fd will be used for this IOCTL? One of the 'vhostfd' or we should > create a new /dev/vhost-workers (or something similar)? >=20 > Maybe the new device will be cleaner and can be reused also for other stu= ff > (I'm thinking about vDPA software devices). >=20 > >=20 > > From a security perspective it means the userspace thread has access to > > all vhost devices (because it has their fds). > >=20 > > I'm not sure how the mm is supposed to work. The devices might be > > associated with different userspace processes (guests) and therefore > > have different virtual memory. >=20 > Maybe in this case we should do something similar to io_uring SQPOLL kthr= ead > where kthread_use_mm()/kthread_unuse_mm() is used to switch virtual memor= y > spaces. >=20 > After writing, I saw that we already do it this in the vhost_worker() in > drivers/vhost/vhost.c >=20 > >=20 > > Just wanted to push this discussion along a little further. I'm buried > > under emails and probably wont be very active over the next few days. > >=20 >=20 > I think ioctl(VHOST_WORKER_RUN) might be the right way and also maybe the > least difficult one. Sending an ioctl API proposal email could help progress this discussion. Interesting questions: 1. How to specify which virtqueues to process (Mike's use case)? 2. How to process multiple devices? Stefan --/WwmFnJnmDyWGHa4 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl/GgMoACgkQnKSrs4Gr c8hCoQf/SoerwKarSrCbMrILigfYpuYZc5i96I08ZMQHTdP2+lpWd0bn+y5JglIl dkket7paJtwxqGLPtyH3TZW3iO608L3tci9Mx/+tUBZLUBipTI9KqMPoseUvS/bQ kyBs7NFFuaLK+XUmaEy73JMY8dU6c/Xl9PC8F1j4FK6Yx+U25bK4M5cSzyZzR/T3 AyroUbt9e9cu6e41wsgCMhQYzXG0rT6V+KUJBhtOWTZ8Oa1AFyiX1SoIaAWUfcgi b+RHSUhamjv87mb7jivsB/XFKDcyceL2LuRcL68UIlXt8rsZDGRmYCpHln9QMPIy fFXgjie3aGN5eVISirSwGny2nFGUfg== =jWcN -----END PGP SIGNATURE----- --/WwmFnJnmDyWGHa4-- 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 X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E5E0C64E7A for ; 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Tue, 1 Dec 2020 17:43:46 +0000 (UTC) Received: from localhost (ovpn-114-82.ams2.redhat.com [10.36.114.82]) by smtp.corp.redhat.com (Postfix) with ESMTP id 58BDC5C1B4; Tue, 1 Dec 2020 17:43:39 +0000 (UTC) Date: Tue, 1 Dec 2020 17:43:38 +0000 From: Stefan Hajnoczi To: Stefano Garzarella Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq Message-ID: <20201201174338.GB595829@stefanha-x1.localdomain> References: <20201118113117.GF182763@stefanha-x1.localdomain> <20201119094315-mutt-send-email-mst@kernel.org> <20201120072802-mutt-send-email-mst@kernel.org> <20201201125943.GE585157@stefanha-x1.localdomain> <20201201134518.pwrggkmixpyro4sg@steredhat> MIME-Version: 1.0 In-Reply-To: <20201201134518.pwrggkmixpyro4sg@steredhat> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="/WwmFnJnmDyWGHa4" Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.497, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: fam , linux-scsi , "Michael S. Tsirkin" , Stefan Hajnoczi , Jason Wang , qemu-devel , Linux Virtualization , target-devel , Paolo Bonzini , Mike Christie Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --/WwmFnJnmDyWGHa4 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Dec 01, 2020 at 02:45:18PM +0100, Stefano Garzarella wrote: > On Tue, Dec 01, 2020 at 12:59:43PM +0000, Stefan Hajnoczi wrote: > > On Fri, Nov 20, 2020 at 07:31:08AM -0500, Michael S. Tsirkin wrote: > > > On Fri, Nov 20, 2020 at 08:45:49AM +0000, Stefan Hajnoczi wrote: > > > > On Thu, Nov 19, 2020 at 5:08 PM Stefan Hajnoczi wrote: > > > > > > > > > > On Thu, Nov 19, 2020 at 4:43 PM Mike Christie > > > > > wrote: > > > > > > > > > > > > On 11/19/20 10:24 AM, Stefan Hajnoczi wrote: > > > > > > > On Thu, Nov 19, 2020 at 4:13 PM Mike Christie > > > > > > > wrote: > > > > > > >> > > > > > > >> On 11/19/20 8:46 AM, Michael S. Tsirkin wrote: > > > > > > >>> On Wed, Nov 18, 2020 at 11:31:17AM +0000, Stefan Hajnoczi w= rote: > > > > > > > struct vhost_run_worker_info { > > > > > > > struct timespec *timeout; > > > > > > > sigset_t *sigmask; > > > > > > > > > > > > > > /* List of virtqueues to process */ > > > > > > > unsigned nvqs; > > > > > > > unsigned vqs[]; > > > > > > > }; > > > > > > > > > > > > > > /* This blocks until the timeout is reached, a signal is rece= ived, or > > > > > > > the vhost device is destroyed */ > > > > > > > int ret =3D ioctl(vhost_fd, VHOST_RUN_WORKER, &info); > > > > > > > > > > > > > > As you can see, userspace isn't involved with dealing with th= e > > > > > > > requests. It just acts as a thread donor to the vhost driver. > > > > > > > > > > > > > > We would want the VHOST_RUN_WORKER calls to be infrequent to = avoid the > > > > > > > penalty of switching into the kernel, copying in the argument= s, etc. > > > > > > > > > > > > I didn't get this part. Why have the timeout? When the timeout = expires, > > > > > > does userspace just call right back down to the kernel or does = it do > > > > > > some sort of processing/operation? > > > > > > > > > > > > You could have your worker function run from that ioctl wait fo= r a > > > > > > signal or a wake up call from the vhost_work/poll functions. > > > > > > > > > > An optional timeout argument is common in blocking interfaces lik= e > > > > > poll(2), recvmmsg(2), etc. > > > > > > > > > > Although something can send a signal to the thread instead, > > > > > implementing that in an application is more awkward than passing = a > > > > > struct timespec. > > > > > > > > > > Compared to other blocking calls we don't expect > > > > > ioctl(VHOST_RUN_WORKER) to return soon, so maybe the timeout will > > > > > rarely be used and can be dropped from the interface. > > > > > > > > > > BTW the code I posted wasn't a carefully thought out proposal :).= The > > > > > details still need to be considered and I'm going to be offline f= or > > > > > the next week so maybe someone else can think it through in the > > > > > meantime. > > > > > > > > One final thought before I'm offline for a week. If > > > > ioctl(VHOST_RUN_WORKER) is specific to a single vhost device instan= ce > > > > then it's hard to support poll-mode (busy waiting) workers because > > > > each device instance consumes a whole CPU. If we stick to an interf= ace > > > > where the kernel manages the worker threads then it's easier to sha= re > > > > workers between devices for polling. > > >=20 > > >=20 > > > Yes that is the reason vhost did its own reason in the first place. > > >=20 > > >=20 > > > I am vaguely thinking about poll(2) or a similar interface, > > > which can wait for an event on multiple FDs. > >=20 > > I can imagine how using poll(2) would work from a userspace perspective= , > > but on the kernel side I don't think it can be implemented cleanly. > > poll(2) is tied to the file_operations->poll() callback and > > read/write/error events. Not to mention there isn't a way to substitue > > the vhost worker thread function instead of scheduling out the current > > thread while waiting for poll fd events. > >=20 > > But maybe ioctl(VHOST_WORKER_RUN) can do it: > >=20 > > struct vhost_run_worker_dev { > > int vhostfd; /* /dev/vhost-TYPE fd */ > > unsigned nvqs; /* number of virtqueues in vqs[] */ > > unsigned vqs[]; /* virtqueues to process */ > > }; > >=20 > > struct vhost_run_worker_info { > > struct timespec *timeout; > > sigset_t *sigmask; > >=20 > > unsigned ndevices; > > struct vhost_run_worker_dev *devices[]; > > }; > >=20 > > In the simple case userspace sets ndevices to 1 and we just handle > > virtqueues for the current device. > >=20 > > In the fancier shared worker thread case the userspace process has the > > vhost fds of all the devices it is processing and passes them to > > ioctl(VHOST_WORKER_RUN) via struct vhost_run_worker_dev elements. >=20 > Which fd will be used for this IOCTL? One of the 'vhostfd' or we should > create a new /dev/vhost-workers (or something similar)? >=20 > Maybe the new device will be cleaner and can be reused also for other stu= ff > (I'm thinking about vDPA software devices). >=20 > >=20 > > From a security perspective it means the userspace thread has access to > > all vhost devices (because it has their fds). > >=20 > > I'm not sure how the mm is supposed to work. The devices might be > > associated with different userspace processes (guests) and therefore > > have different virtual memory. >=20 > Maybe in this case we should do something similar to io_uring SQPOLL kthr= ead > where kthread_use_mm()/kthread_unuse_mm() is used to switch virtual memor= y > spaces. >=20 > After writing, I saw that we already do it this in the vhost_worker() in > drivers/vhost/vhost.c >=20 > >=20 > > Just wanted to push this discussion along a little further. I'm buried > > under emails and probably wont be very active over the next few days. > >=20 >=20 > I think ioctl(VHOST_WORKER_RUN) might be the right way and also maybe the > least difficult one. Sending an ioctl API proposal email could help progress this discussion. Interesting questions: 1. How to specify which virtqueues to process (Mike's use case)? 2. How to process multiple devices? Stefan --/WwmFnJnmDyWGHa4 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl/GgMoACgkQnKSrs4Gr c8hCoQf/SoerwKarSrCbMrILigfYpuYZc5i96I08ZMQHTdP2+lpWd0bn+y5JglIl dkket7paJtwxqGLPtyH3TZW3iO608L3tci9Mx/+tUBZLUBipTI9KqMPoseUvS/bQ kyBs7NFFuaLK+XUmaEy73JMY8dU6c/Xl9PC8F1j4FK6Yx+U25bK4M5cSzyZzR/T3 AyroUbt9e9cu6e41wsgCMhQYzXG0rT6V+KUJBhtOWTZ8Oa1AFyiX1SoIaAWUfcgi b+RHSUhamjv87mb7jivsB/XFKDcyceL2LuRcL68UIlXt8rsZDGRmYCpHln9QMPIy fFXgjie3aGN5eVISirSwGny2nFGUfg== =jWcN -----END PGP SIGNATURE----- --/WwmFnJnmDyWGHa4-- 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 X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E548C64E7B for ; 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Tue, 1 Dec 2020 17:43:46 +0000 (UTC) Received: from localhost (ovpn-114-82.ams2.redhat.com [10.36.114.82]) by smtp.corp.redhat.com (Postfix) with ESMTP id 58BDC5C1B4; Tue, 1 Dec 2020 17:43:39 +0000 (UTC) Date: Tue, 1 Dec 2020 17:43:38 +0000 From: Stefan Hajnoczi To: Stefano Garzarella Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq Message-ID: <20201201174338.GB595829@stefanha-x1.localdomain> References: <20201118113117.GF182763@stefanha-x1.localdomain> <20201119094315-mutt-send-email-mst@kernel.org> <20201120072802-mutt-send-email-mst@kernel.org> <20201201125943.GE585157@stefanha-x1.localdomain> <20201201134518.pwrggkmixpyro4sg@steredhat> MIME-Version: 1.0 In-Reply-To: <20201201134518.pwrggkmixpyro4sg@steredhat> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Cc: fam , linux-scsi , "Michael S. Tsirkin" , qemu-devel , Linux Virtualization , target-devel , Paolo Bonzini , Mike Christie X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: multipart/mixed; boundary="===============3918954081615172418==" Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" --===============3918954081615172418== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="/WwmFnJnmDyWGHa4" Content-Disposition: inline --/WwmFnJnmDyWGHa4 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Dec 01, 2020 at 02:45:18PM +0100, Stefano Garzarella wrote: > On Tue, Dec 01, 2020 at 12:59:43PM +0000, Stefan Hajnoczi wrote: > > On Fri, Nov 20, 2020 at 07:31:08AM -0500, Michael S. Tsirkin wrote: > > > On Fri, Nov 20, 2020 at 08:45:49AM +0000, Stefan Hajnoczi wrote: > > > > On Thu, Nov 19, 2020 at 5:08 PM Stefan Hajnoczi wrote: > > > > > > > > > > On Thu, Nov 19, 2020 at 4:43 PM Mike Christie > > > > > wrote: > > > > > > > > > > > > On 11/19/20 10:24 AM, Stefan Hajnoczi wrote: > > > > > > > On Thu, Nov 19, 2020 at 4:13 PM Mike Christie > > > > > > > wrote: > > > > > > >> > > > > > > >> On 11/19/20 8:46 AM, Michael S. Tsirkin wrote: > > > > > > >>> On Wed, Nov 18, 2020 at 11:31:17AM +0000, Stefan Hajnoczi w= rote: > > > > > > > struct vhost_run_worker_info { > > > > > > > struct timespec *timeout; > > > > > > > sigset_t *sigmask; > > > > > > > > > > > > > > /* List of virtqueues to process */ > > > > > > > unsigned nvqs; > > > > > > > unsigned vqs[]; > > > > > > > }; > > > > > > > > > > > > > > /* This blocks until the timeout is reached, a signal is rece= ived, or > > > > > > > the vhost device is destroyed */ > > > > > > > int ret =3D ioctl(vhost_fd, VHOST_RUN_WORKER, &info); > > > > > > > > > > > > > > As you can see, userspace isn't involved with dealing with th= e > > > > > > > requests. It just acts as a thread donor to the vhost driver. > > > > > > > > > > > > > > We would want the VHOST_RUN_WORKER calls to be infrequent to = avoid the > > > > > > > penalty of switching into the kernel, copying in the argument= s, etc. > > > > > > > > > > > > I didn't get this part. Why have the timeout? When the timeout = expires, > > > > > > does userspace just call right back down to the kernel or does = it do > > > > > > some sort of processing/operation? > > > > > > > > > > > > You could have your worker function run from that ioctl wait fo= r a > > > > > > signal or a wake up call from the vhost_work/poll functions. > > > > > > > > > > An optional timeout argument is common in blocking interfaces lik= e > > > > > poll(2), recvmmsg(2), etc. > > > > > > > > > > Although something can send a signal to the thread instead, > > > > > implementing that in an application is more awkward than passing = a > > > > > struct timespec. > > > > > > > > > > Compared to other blocking calls we don't expect > > > > > ioctl(VHOST_RUN_WORKER) to return soon, so maybe the timeout will > > > > > rarely be used and can be dropped from the interface. > > > > > > > > > > BTW the code I posted wasn't a carefully thought out proposal :).= The > > > > > details still need to be considered and I'm going to be offline f= or > > > > > the next week so maybe someone else can think it through in the > > > > > meantime. > > > > > > > > One final thought before I'm offline for a week. If > > > > ioctl(VHOST_RUN_WORKER) is specific to a single vhost device instan= ce > > > > then it's hard to support poll-mode (busy waiting) workers because > > > > each device instance consumes a whole CPU. If we stick to an interf= ace > > > > where the kernel manages the worker threads then it's easier to sha= re > > > > workers between devices for polling. > > >=20 > > >=20 > > > Yes that is the reason vhost did its own reason in the first place. > > >=20 > > >=20 > > > I am vaguely thinking about poll(2) or a similar interface, > > > which can wait for an event on multiple FDs. > >=20 > > I can imagine how using poll(2) would work from a userspace perspective= , > > but on the kernel side I don't think it can be implemented cleanly. > > poll(2) is tied to the file_operations->poll() callback and > > read/write/error events. Not to mention there isn't a way to substitue > > the vhost worker thread function instead of scheduling out the current > > thread while waiting for poll fd events. > >=20 > > But maybe ioctl(VHOST_WORKER_RUN) can do it: > >=20 > > struct vhost_run_worker_dev { > > int vhostfd; /* /dev/vhost-TYPE fd */ > > unsigned nvqs; /* number of virtqueues in vqs[] */ > > unsigned vqs[]; /* virtqueues to process */ > > }; > >=20 > > struct vhost_run_worker_info { > > struct timespec *timeout; > > sigset_t *sigmask; > >=20 > > unsigned ndevices; > > struct vhost_run_worker_dev *devices[]; > > }; > >=20 > > In the simple case userspace sets ndevices to 1 and we just handle > > virtqueues for the current device. > >=20 > > In the fancier shared worker thread case the userspace process has the > > vhost fds of all the devices it is processing and passes them to > > ioctl(VHOST_WORKER_RUN) via struct vhost_run_worker_dev elements. >=20 > Which fd will be used for this IOCTL? One of the 'vhostfd' or we should > create a new /dev/vhost-workers (or something similar)? >=20 > Maybe the new device will be cleaner and can be reused also for other stu= ff > (I'm thinking about vDPA software devices). >=20 > >=20 > > From a security perspective it means the userspace thread has access to > > all vhost devices (because it has their fds). > >=20 > > I'm not sure how the mm is supposed to work. The devices might be > > associated with different userspace processes (guests) and therefore > > have different virtual memory. >=20 > Maybe in this case we should do something similar to io_uring SQPOLL kthr= ead > where kthread_use_mm()/kthread_unuse_mm() is used to switch virtual memor= y > spaces. >=20 > After writing, I saw that we already do it this in the vhost_worker() in > drivers/vhost/vhost.c >=20 > >=20 > > Just wanted to push this discussion along a little further. I'm buried > > under emails and probably wont be very active over the next few days. > >=20 >=20 > I think ioctl(VHOST_WORKER_RUN) might be the right way and also maybe the > least difficult one. Sending an ioctl API proposal email could help progress this discussion. Interesting questions: 1. How to specify which virtqueues to process (Mike's use case)? 2. How to process multiple devices? Stefan --/WwmFnJnmDyWGHa4 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl/GgMoACgkQnKSrs4Gr c8hCoQf/SoerwKarSrCbMrILigfYpuYZc5i96I08ZMQHTdP2+lpWd0bn+y5JglIl dkket7paJtwxqGLPtyH3TZW3iO608L3tci9Mx/+tUBZLUBipTI9KqMPoseUvS/bQ kyBs7NFFuaLK+XUmaEy73JMY8dU6c/Xl9PC8F1j4FK6Yx+U25bK4M5cSzyZzR/T3 AyroUbt9e9cu6e41wsgCMhQYzXG0rT6V+KUJBhtOWTZ8Oa1AFyiX1SoIaAWUfcgi b+RHSUhamjv87mb7jivsB/XFKDcyceL2LuRcL68UIlXt8rsZDGRmYCpHln9QMPIy fFXgjie3aGN5eVISirSwGny2nFGUfg== =jWcN -----END PGP SIGNATURE----- --/WwmFnJnmDyWGHa4-- --===============3918954081615172418== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization --===============3918954081615172418==--