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Date: Wed, 8 May 2024 11:43:52 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: netdev@...r.kernel.org,
virtualization@...ts.linux.dev,
"Michael S . Tsirkin" <mst@...hat.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
Eric Dumazet <edumazet@...gle.com>,
"David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next 1/3] virtio_net: enable irq for the control vq
On Wed, 8 May 2024 10:19:06 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Tue, May 7, 2024 at 2:33 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> >
> > On Tue, 7 May 2024 14:24:16 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > > On Tue, May 7, 2024 at 12:03 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> > > >
> > > > On Tue, 7 May 2024 11:15:22 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > > > > On Thu, Apr 25, 2024 at 8:59 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> > > > > >
> > > > > > Control vq polling request results consume more CPU.
> > > > > > Especially when dim issues more control requests to the device,
> > > > > > it's beneficial to the guest to enable control vq's irq.
> > > > > >
> > > > > > Suggested-by: Jason Wang <jasowang@...hat.com>
> > > > > > Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> > > > > > ---
> > > > > > drivers/net/virtio_net.c | 45 ++++++++++++++++++++++++++++++----------
> > > > > > 1 file changed, 34 insertions(+), 11 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > > > index a4d3c76654a4..79a1b30c173c 100644
> > > > > > --- a/drivers/net/virtio_net.c
> > > > > > +++ b/drivers/net/virtio_net.c
> > > > > > @@ -287,6 +287,12 @@ struct virtnet_info {
> > > > > > bool has_cvq;
> > > > > > struct mutex cvq_lock;
> > > > > >
> > > > > > + /* Wait for the device to complete the request */
> > > > > > + struct completion completion;
> > > > > > +
> > > > > > + /* Work struct for acquisition of cvq processing results. */
> > > > > > + struct work_struct get_cvq;
> > > > > > +
> > > > > > /* Host can handle any s/g split between our header and packet data */
> > > > > > bool any_header_sg;
> > > > > >
> > > > > > @@ -520,6 +526,13 @@ static bool virtqueue_napi_complete(struct napi_struct *napi,
> > > > > > return false;
> > > > > > }
> > > > > >
> > > > > > +static void virtnet_cvq_done(struct virtqueue *cvq)
> > > > > > +{
> > > > > > + struct virtnet_info *vi = cvq->vdev->priv;
> > > > > > +
> > > > > > + schedule_work(&vi->get_cvq);
> > > > > > +}
> > > > > > +
> > > > > > static void skb_xmit_done(struct virtqueue *vq)
> > > > > > {
> > > > > > struct virtnet_info *vi = vq->vdev->priv;
> > > > > > @@ -2036,6 +2049,20 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
> > > > > > return !oom;
> > > > > > }
> > > > > >
> > > > > > +static void virtnet_get_cvq_work(struct work_struct *work)
> > > > > > +{
> > > > > > + struct virtnet_info *vi =
> > > > > > + container_of(work, struct virtnet_info, get_cvq);
> > > > > > + unsigned int tmp;
> > > > > > + void *res;
> > > > > > +
> > > > > > + mutex_lock(&vi->cvq_lock);
> > > > > > + res = virtqueue_get_buf(vi->cvq, &tmp);
> > > > > > + if (res)
> > > > > > + complete(&vi->completion);
> > > > > > + mutex_unlock(&vi->cvq_lock);
> > > > > > +}
> > > > > > +
> > > > > > static void skb_recv_done(struct virtqueue *rvq)
> > > > > > {
> > > > > > struct virtnet_info *vi = rvq->vdev->priv;
> > > > > > @@ -2531,7 +2558,7 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> > > > > > struct scatterlist *out)
> > > > > > {
> > > > > > struct scatterlist *sgs[4], hdr, stat;
> > > > > > - unsigned out_num = 0, tmp;
> > > > > > + unsigned out_num = 0;
> > > > > > int ret;
> > > > > >
> > > > > > /* Caller should know better */
> > > > > > @@ -2566,16 +2593,10 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> > > > > > 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)) {
> > > > > > - cond_resched();
> > > > > > - cpu_relax();
> > > > > > - }
> > > > > > -
> > > > > > mutex_unlock(&vi->cvq_lock);
> > > > > > +
> > > > > > + wait_for_completion(&vi->completion);
> > > > > > +
> > > > >
> > > > > A question here, can multiple cvq requests be submitted to the device?
> > > > > If yes, what happens if the device completes them out of order?
> > > >
> > > > For user commands (such as ethtool cmds), multiple cvq requests is not allowed.
> > > > because it holds the netlink lock when waiting for the response.
> > > >
> > > > For multiple dim commands and a user command allowed to be sent simultaneously
> > > > , the corresponding command-specific information(desc_state) will be used to
> > > > distinguish different responses.
> > >
> > > Just to make sure we are on the same page. I meant at least we are
> > > still use the global completion which seems to be problematic.
> > >
> > > wait_for_completion(&vi->completion);
> >
> >
> > This completion is only used by the ethtool command, so it is the global one.
> >
> > dim commands use specific coal_free_list and coal_wait_list to complete
> > multiple command issuance (please see patch 3).
>
> If I was not wrong, at least for this patch the global completion will
> be used by both dim and rtnl. If yes, it's not good to introduce a bug
> in patch 1 and fix it in patch 3.
Ok, patches 1 and 3 will be refactored.
Thanks.
>
> Thanks
>
> >
> > Thanks.
> >
> > >
> > > Thanks
> > >
> > >
> > > >
> > > > Thanks.
> > > >
> > > > >
> > > > > Thanks
> > > > >
> > > > > > return vi->ctrl->status == VIRTIO_NET_OK;
> > > > > > }
> > > > > >
> > > > > > @@ -4433,7 +4454,7 @@ 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";
> > > > > > }
> > > > > >
> > > > > > @@ -4952,6 +4973,8 @@ static int virtnet_probe(struct virtio_device *vdev)
> > > > > > if (vi->has_rss || vi->has_rss_hash_report)
> > > > > > virtnet_init_default_rss(vi);
> > > > > >
> > > > > > + INIT_WORK(&vi->get_cvq, virtnet_get_cvq_work);
> > > > > > + init_completion(&vi->completion);
> > > > > > enable_rx_mode_work(vi);
> > > > > >
> > > > > > /* serialize netdev register + virtio_device_ready() with ndo_open() */
> > > > > > --
> > > > > > 2.32.0.3.g01195cf9f
> > > > > >
> > > > >
> > > >
> > >
> >
>
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