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SubjectRe: [PATCH net-next v4 2/2] virtio-net: add cond_resched() to the command waiting loop
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On 7/20/23 23:02, Michael S. Tsirkin wrote:
> On Thu, Jul 20, 2023 at 01:26:20PM -0700, Shannon Nelson wrote:
>> 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@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@amd.com>
>>
>
> I'd like to see a full solution
> 1- block until interrupt

Would it make sense to also have a timeout?
And when timeout expires, set FAILED bit in device status?

> 2- still handle surprise removal correctly by waking in that case
>
>
>
>>> ---
>>> 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@lists.linux-foundation.org
>>> https://lists.linuxfoundation.org/mailman/listinfo/virtualization
>

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