Michael S. Tsirkin
2022-Sep-05 07:15 UTC
[PATCH net] virtio-net: add cond_resched() to the command waiting loop
On Mon, Sep 05, 2022 at 12:53:41PM +0800, Jason Wang wrote:> Adding cond_resched() to the command waiting loop for a better > co-operation with the scheduler. This allows to give CPU a breath to > run other task(workqueue) instead of busy looping when preemption is > not allowed. > > What's more important. This is a must for some vDPA parent to work > since control virtqueue is emulated via a workqueue for those parents. > > Fixes: bda324fd037a ("vdpasim: control virtqueue support")That's a weird commit to fix. so it fixes the simulator?> Signed-off-by: Jason Wang <jasowang at redhat.com> > --- > drivers/net/virtio_net.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index ece00b84e3a7..169368365d6a 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -2000,8 +2000,10 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd, > * into the hypervisor, so the request should be handled immediately. > */ > while (!virtqueue_get_buf(vi->cvq, &tmp) && > - !virtqueue_is_broken(vi->cvq)) > + !virtqueue_is_broken(vi->cvq)) { > + cond_resched(); > cpu_relax(); > + }with cond_resched do we still need cpu_relax?> return vi->ctrl->status == VIRTIO_NET_OK; > } > -- > 2.25.1
Jason Wang
2022-Sep-05 07:49 UTC
[PATCH net] virtio-net: add cond_resched() to the command waiting loop
On Mon, Sep 5, 2022 at 3:15 PM Michael S. Tsirkin <mst at redhat.com> wrote:> > On Mon, Sep 05, 2022 at 12:53:41PM +0800, Jason Wang wrote: > > Adding cond_resched() to the command waiting loop for a better > > co-operation with the scheduler. This allows to give CPU a breath to > > run other task(workqueue) instead of busy looping when preemption is > > not allowed. > > > > What's more important. This is a must for some vDPA parent to work > > since control virtqueue is emulated via a workqueue for those parents. > > > > Fixes: bda324fd037a ("vdpasim: control virtqueue support") > > That's a weird commit to fix. so it fixes the simulator?Yes, since the simulator is using a workqueue to handle control virtueue.> > > Signed-off-by: Jason Wang <jasowang at redhat.com> > > --- > > drivers/net/virtio_net.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index ece00b84e3a7..169368365d6a 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -2000,8 +2000,10 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd, > > * into the hypervisor, so the request should be handled immediately. > > */ > > while (!virtqueue_get_buf(vi->cvq, &tmp) && > > - !virtqueue_is_broken(vi->cvq)) > > + !virtqueue_is_broken(vi->cvq)) { > > + cond_resched(); > > cpu_relax(); > > + } > > with cond_resched do we still need cpu_relax?I think so, it's possible that cond_sched() just doesn't trigger scheduling. Thanks> > > return vi->ctrl->status == VIRTIO_NET_OK; > > } > > -- > > 2.25.1 >