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Tsirkin" Cc: Heng Qi , Jason Wang , netdev@vger.kernel.org, virtualization@lists.linux.dev, Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Subject: Re: [PATCH net-next v4 2/5] virtio_net: enable irq for the control vq Message-ID: References: <20240619171708-mutt-send-email-mst@kernel.org> <1718868555.2701075-5-hengqi@linux.alibaba.com> <1718877195.0503237-9-hengqi@linux.alibaba.com> <20240620060816-mutt-send-email-mst@kernel.org> <20240620061109-mutt-send-email-mst@kernel.org> <1718879494.952194-11-hengqi@linux.alibaba.com> <20240626040730-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240626040730-mutt-send-email-mst@kernel.org> Wed, Jun 26, 2024 at 10:08:14AM CEST, mst@redhat.com wrote: >On Wed, Jun 26, 2024 at 09:52:58AM +0200, Jiri Pirko wrote: >> Thu, Jun 20, 2024 at 12:31:34PM CEST, hengqi@linux.alibaba.com wrote: >> >On Thu, 20 Jun 2024 06:11:40 -0400, "Michael S. Tsirkin" wrote: >> >> On Thu, Jun 20, 2024 at 06:10:51AM -0400, Michael S. Tsirkin wrote: >> >> > On Thu, Jun 20, 2024 at 05:53:15PM +0800, Heng Qi wrote: >> >> > > On Thu, 20 Jun 2024 16:26:05 +0800, Jason Wang wrote: >> >> > > > On Thu, Jun 20, 2024 at 4:21 PM Jason Wang wrote: >> >> > > > > >> >> > > > > On Thu, Jun 20, 2024 at 3:35 PM Heng Qi wrote: >> >> > > > > > >> >> > > > > > On Wed, 19 Jun 2024 17:19:12 -0400, "Michael S. Tsirkin" wrote: >> >> > > > > > > On Thu, Jun 20, 2024 at 12:19:05AM +0800, Heng Qi wrote: >> >> > > > > > > > @@ -5312,7 +5315,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi) >> >> > > > > > > > >> >> > > > > > > > /* Parameters for control virtqueue, if any */ >> >> > > > > > > > if (vi->has_cvq) { >> >> > > > > > > > - callbacks[total_vqs - 1] = NULL; >> >> > > > > > > > + callbacks[total_vqs - 1] = virtnet_cvq_done; >> >> > > > > > > > names[total_vqs - 1] = "control"; >> >> > > > > > > > } >> >> > > > > > > > >> >> > > > > > > >> >> > > > > > > If the # of MSIX vectors is exactly for data path VQs, >> >> > > > > > > this will cause irq sharing between VQs which will degrade >> >> > > > > > > performance significantly. >> >> > > > > > > >> >> > > > > >> >> > > > > Why do we need to care about buggy management? I think libvirt has >> >> > > > > been teached to use 2N+2 since the introduction of the multiqueue[1]. >> >> > > > >> >> > > > And Qemu can calculate it correctly automatically since: >> >> > > > >> >> > > > commit 51a81a2118df0c70988f00d61647da9e298483a4 >> >> > > > Author: Jason Wang >> >> > > > Date: Mon Mar 8 12:49:19 2021 +0800 >> >> > > > >> >> > > > virtio-net: calculating proper msix vectors on init >> >> > > > >> >> > > > Currently, the default msix vectors for virtio-net-pci is 3 which is >> >> > > > obvious not suitable for multiqueue guest, so we depends on the user >> >> > > > or management tools to pass a correct vectors parameter. In fact, we >> >> > > > can simplifying this by calculating the number of vectors on realize. >> >> > > > >> >> > > > Consider we have N queues, the number of vectors needed is 2*N + 2 >> >> > > > (#queue pairs + plus one config interrupt and control vq). We didn't >> >> > > > check whether or not host support control vq because it was added >> >> > > > unconditionally by qemu to avoid breaking legacy guests such as Minix. >> >> > > > >> >> > > > Reviewed-by: Philippe Mathieu-Daudé > >> > > > Reviewed-by: Stefano Garzarella >> >> > > > Reviewed-by: Stefan Hajnoczi >> >> > > > Signed-off-by: Jason Wang >> >> > > >> >> > > Yes, devices designed according to the spec need to reserve an interrupt >> >> > > vector for ctrlq. So, Michael, do we want to be compatible with buggy devices? >> >> > > >> >> > > Thanks. >> >> > >> >> > These aren't buggy, the spec allows this. So don't fail, but >> >> > I'm fine with using polling if not enough vectors. >> >> >> >> sharing with config interrupt is easier code-wise though, FWIW - >> >> we don't need to maintain two code-paths. >> > >> >Yes, it works well - config change irq is used less before - and will not fail. >> >> Please note I'm working on such fallback for admin queue. I would Like >> to send the patchset by the end of this week. You can then use it easily >> for cvq. >> >> Something like: >> /* the config->find_vqs() implementation */ >> int vp_find_vqs(struct virtio_device *vdev, unsigned int nvqs, >> struct virtqueue *vqs[], vq_callback_t *callbacks[], >> const char * const names[], const bool *ctx, >> struct irq_affinity *desc) >> { >> int err; >> >> /* Try MSI-X with one vector per queue. */ >> err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, >> VP_VQ_VECTOR_POLICY_EACH, ctx, desc); >> if (!err) >> return 0; >> /* Fallback: MSI-X with one shared vector for config and >> * slow path queues, one vector per queue for the rest. */ >> err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, >> VP_VQ_VECTOR_POLICY_SHARED_SLOW, ctx, desc); >> if (!err) >> return 0; >> /* Fallback: MSI-X with one vector for config, one shared for queues. */ >> err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, >> VP_VQ_VECTOR_POLICY_SHARED, ctx, desc); >> if (!err) >> return 0; >> /* Is there an interrupt? If not give up. */ >> if (!(to_vp_device(vdev)->pci_dev->irq)) >> return err; >> /* Finally fall back to regular interrupts. */ >> return vp_find_vqs_intx(vdev, nvqs, vqs, callbacks, names, ctx); >> } >> >> > > >Well for cvq, we'll need to adjust the API so core >knows cvq interrupts are be shared with config not >datapath. Agreed. I was thinking about introducing some info struct and pass array of it instead of callbacks[] and names[]. Then the struct can contain flag indication. Something like: struct vq_info { vq_callback_t *callback; const char *name; bool slow_path; }; > > > >> >> > >> >Thanks. >> > >> >> >> >> > > > >> >> > > > Thanks >> >> > > > >> >> > > > > >> >> > > > > > > So no, you can not just do it unconditionally. >> >> > > > > > > >> >> > > > > > > The correct fix probably requires virtio core/API extensions. >> >> > > > > > >> >> > > > > > If the introduction of cvq irq causes interrupts to become shared, then >> >> > > > > > ctrlq need to fall back to polling mode and keep the status quo. >> >> > > > > >> >> > > > > Having to path sounds a burden. >> >> > > > > >> >> > > > > > >> >> > > > > > Thanks. >> >> > > > > > >> >> > > > > >> >> > > > > >> >> > > > > Thanks >> >> > > > > >> >> > > > > [1] https://www.linux-kvm.org/page/Multiqueue >> >> > > > > >> >> > > > > > > >> >> > > > > > > -- >> >> > > > > > > MST >> >> > > > > > > >> >> > > > > > >> >> > > > >> >> >> > >