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Tsirkin" To: Jason Wang Subject: Re: [PATCH net-next V2 2/2] virtio-net: sleep instead of busy waiting for cvq command Message-ID: <20230516165043-mutt-send-email-mst@kernel.org> References: <20230413064027.13267-1-jasowang@redhat.com> <20230413064027.13267-3-jasowang@redhat.com> MIME-Version: 1.0 In-Reply-To: <20230413064027.13267-3-jasowang@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: xuanzhuo@linux.alibaba.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, eperezma@redhat.com, edumazet@google.com, maxime.coquelin@redhat.com, kuba@kernel.org, pabeni@redhat.com, david.marchand@redhat.com, davem@davemloft.net 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: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Thu, Apr 13, 2023 at 02:40:27PM +0800, Jason Wang wrote: > We used to busy waiting on the cvq command this tends to be > problematic since there no way for to schedule another process which > may serve for the control virtqueue. This might be the case when the > control virtqueue is emulated by software. This patch switches to use > completion to allow the CPU to sleep instead of busy waiting for the > cvq command. > > Signed-off-by: Jason Wang > --- > Changes since V1: > - use completion for simplicity > - don't try to harden the CVQ command which requires more thought > Changes since RFC: > - break the device when timeout > - get buffer manually since the virtio core check more_used() instead > --- > drivers/net/virtio_net.c | 21 ++++++++++++++------- > 1 file changed, 14 insertions(+), 7 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 2e56bbf86894..d3eb8fd6c9dc 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -19,6 +19,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -295,6 +296,8 @@ struct virtnet_info { > > /* failover when STANDBY feature enabled */ > struct failover *failover; > + > + struct completion completion; > }; > > struct padded_vnet_hdr { > @@ -1709,6 +1712,13 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq, > return !oom; > } > > +static void virtnet_cvq_done(struct virtqueue *cvq) > +{ > + struct virtnet_info *vi = cvq->vdev->priv; > + > + complete(&vi->completion); > +} > + > static void skb_recv_done(struct virtqueue *rvq) > { > struct virtnet_info *vi = rvq->vdev->priv; > @@ -2169,12 +2179,8 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd, > if (unlikely(!virtqueue_kick(vi->cvq))) > return vi->ctrl->status == VIRTIO_NET_OK; > > - /* Spin for a response, the kick causes an ioport write, trapping > - * into the hypervisor, so the request should be handled immediately. > - */ > - while (!virtqueue_get_buf(vi->cvq, &tmp) && > - !virtqueue_is_broken(vi->cvq)) > - cpu_relax(); > + wait_for_completion(&vi->completion); > + virtqueue_get_buf(vi->cvq, &tmp); > > return vi->ctrl->status == VIRTIO_NET_OK; This seems to break surprise removal and other situations where vq gets broken since callbacks aren't usually invoked then. > } > @@ -3672,7 +3678,7 @@ 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"; > } > There is a cost to this, in that we are burning an extra MSI vector for the slow path cvq. if device has 3 vectors, suddenly we can't allocate vectors for rx and tx, big problem. So I'm afraid we need to pass a new flag that will share the config changed interrupt and cvq. > @@ -4122,6 +4128,7 @@ static int virtnet_probe(struct virtio_device *vdev) > if (vi->has_rss || vi->has_rss_hash_report) > virtnet_init_default_rss(vi); > > + init_completion(&vi->completion); > enable_rx_mode_work(vi); > > /* serialize netdev register + virtio_device_ready() with ndo_open() */ > -- > 2.25.1 _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization