Jason Wang
2022-Sep-05 04:53 UTC
[PATCH net] virtio-net: add cond_resched() to the command waiting loop
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")
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();
+ }
return vi->ctrl->status == VIRTIO_NET_OK;
}
--
2.25.1
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
Michael S. Tsirkin
2022-Oct-17 20:09 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") > Signed-off-by: Jason Wang <jasowang at redhat.com>Acked-by: Michael S. Tsirkin <mst 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(); > + } > > return vi->ctrl->status == VIRTIO_NET_OK; > } > -- > 2.25.1