Jason Wang
2023-Jul-20 08:38 UTC
[PATCH net-next v4 2/2] 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 on a device whose CVQ might be slow.
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 9f3b1d6ac33d..e7533f29b219 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2314,8 +2314,10 @@ 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;
}
--
2.39.3
Shannon Nelson
2023-Jul-20 15:31 UTC
[PATCH net-next v4 2/2] virtio-net: add cond_resched() to the command waiting loop
On 7/20/23 1:38 AM, 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 on a device whose CVQ might be slow. > > 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 9f3b1d6ac33d..e7533f29b219 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -2314,8 +2314,10 @@ 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(); > + }The cover letter suggests that this addresses the infinite poll for buggy devices, but I don't see how that is resolved here. This should make it a little nicer to the system, but it still is going to poll forever on a device that has gone catatonic. Is there a reason that I'm missing that we don't have a polling limit here? sln> > return vi->ctrl->status == VIRTIO_NET_OK; > } > -- > 2.39.3 > > _______________________________________________ > Virtualization mailing list > Virtualization at lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Shannon Nelson
2023-Jul-20 20:26 UTC
[PATCH net-next v4 2/2] virtio-net: add cond_resched() to the command waiting loop
On 7/20/23 1:38 AM, 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 on a device whose CVQ might be slow. > > Signed-off-by: Jason Wang <jasowang at redhat.com>This still leaves hung processes, but at least it doesn't pin the CPU any more. Thanks. Reviewed-by: Shannon Nelson <shannon.nelson at amd.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 9f3b1d6ac33d..e7533f29b219 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -2314,8 +2314,10 @@ 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; > } > -- > 2.39.3 > > _______________________________________________ > Virtualization mailing list > Virtualization at lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/virtualization