Messages in this thread | | | Date | Fri, 21 Jul 2023 16:58:04 +0200 | Subject | Re: [PATCH net-next v4 2/2] virtio-net: add cond_resched() to the command waiting loop | From | Maxime Coquelin <> |
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On 7/21/23 16:45, Michael S. Tsirkin wrote: > On Fri, Jul 21, 2023 at 04:37:00PM +0200, Maxime Coquelin wrote: >> >> >> 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? > > virtio spec does not set any limits on the timing of vq > processing.
Indeed, but I thought the driver could decide it is too long for it.
The issue is we keep waiting with rtnl locked, it can quickly make the system unusable.
>>> 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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