* network performance degradation in virtio_net in 4.12-rc
@ 2017-05-22 14:25 Mikulas Patocka
2017-05-22 17:42 ` Michael S. Tsirkin
2017-05-22 17:42 ` Michael S. Tsirkin
0 siblings, 2 replies; 5+ messages in thread
From: Mikulas Patocka @ 2017-05-22 14:25 UTC (permalink / raw)
To: Michael S. Tsirkin, Jason Wang; +Cc: kvm, virtualization, netdev
Hi
I see severe network performance degradation with the kernels 4.12-rc1 and
4.12-rc2 in the network virtio driver. Download rate drops down to about
100kB/s.
I bisected it and it is caused by patch
d85b758f72b05a774045545f24d70980e3e9aac4 ("virtio_net: fix support for
small rings"). When I revert this patch, the problem goes away.
The host is Debian Jessie with kernel 4.4.62, the guest is Debian Sid with
kernel 4.12-rc.
Mikulas
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: network performance degradation in virtio_net in 4.12-rc
2017-05-22 14:25 network performance degradation in virtio_net in 4.12-rc Mikulas Patocka
@ 2017-05-22 17:42 ` Michael S. Tsirkin
2017-05-22 21:50 ` Mikulas Patocka
2017-05-22 17:42 ` Michael S. Tsirkin
1 sibling, 1 reply; 5+ messages in thread
From: Michael S. Tsirkin @ 2017-05-22 17:42 UTC (permalink / raw)
To: Mikulas Patocka; +Cc: Jason Wang, kvm, virtualization, netdev
On Mon, May 22, 2017 at 10:25:19AM -0400, Mikulas Patocka wrote:
> Hi
>
> I see severe network performance degradation with the kernels 4.12-rc1 and
> 4.12-rc2 in the network virtio driver. Download rate drops down to about
> 100kB/s.
>
> I bisected it and it is caused by patch
> d85b758f72b05a774045545f24d70980e3e9aac4 ("virtio_net: fix support for
> small rings"). When I revert this patch, the problem goes away.
>
> The host is Debian Jessie with kernel 4.4.62, the guest is Debian Sid with
> kernel 4.12-rc.
>
> Mikulas
Thanks for the report!
I'm not sure what causes it on this host. I'll try to reproduce.
Meanwhile, could you please locate this line of code:
+ vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
and add something like
printk(KERN_ERR, "min buf = 0x%x expected 0x%x size 0x%x big %d\n",
vi->rq[i].min_buf_len, GOOD_PACKET_LEN,
virtqueue_get_vring_size(vi->rq[i].vq),
(int)vi->big_packets);
after it?
Then boot and capture the output.
Thanks!
--
MST
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: network performance degradation in virtio_net in 4.12-rc
2017-05-22 17:42 ` Michael S. Tsirkin
@ 2017-05-22 21:50 ` Mikulas Patocka
0 siblings, 0 replies; 5+ messages in thread
From: Mikulas Patocka @ 2017-05-22 21:50 UTC (permalink / raw)
To: Michael S. Tsirkin; +Cc: netdev, kvm, virtualization
On Mon, 22 May 2017, Michael S. Tsirkin wrote:
> On Mon, May 22, 2017 at 10:25:19AM -0400, Mikulas Patocka wrote:
> > Hi
> >
> > I see severe network performance degradation with the kernels 4.12-rc1 and
> > 4.12-rc2 in the network virtio driver. Download rate drops down to about
> > 100kB/s.
> >
> > I bisected it and it is caused by patch
> > d85b758f72b05a774045545f24d70980e3e9aac4 ("virtio_net: fix support for
> > small rings"). When I revert this patch, the problem goes away.
> >
> > The host is Debian Jessie with kernel 4.4.62, the guest is Debian Sid with
> > kernel 4.12-rc.
> >
> > Mikulas
>
> Thanks for the report!
> I'm not sure what causes it on this host. I'll try to reproduce.
> Meanwhile, could you please locate this line of code:
> + vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
>
> and add something like
> printk(KERN_ERR, "min buf = 0x%x expected 0x%x size 0x%x big %d\n",
> vi->rq[i].min_buf_len, GOOD_PACKET_LEN,
> virtqueue_get_vring_size(vi->rq[i].vq),
> (int)vi->big_packets);
>
> after it?
> Then boot and capture the output.
>
> Thanks!
It prints one line "min buf = 0x101 expected 0x5ee size 0x100 big 1".
Mikulas
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: network performance degradation in virtio_net in 4.12-rc
2017-05-22 14:25 network performance degradation in virtio_net in 4.12-rc Mikulas Patocka
2017-05-22 17:42 ` Michael S. Tsirkin
@ 2017-05-22 17:42 ` Michael S. Tsirkin
1 sibling, 0 replies; 5+ messages in thread
From: Michael S. Tsirkin @ 2017-05-22 17:42 UTC (permalink / raw)
To: Mikulas Patocka; +Cc: netdev, kvm, virtualization
On Mon, May 22, 2017 at 10:25:19AM -0400, Mikulas Patocka wrote:
> Hi
>
> I see severe network performance degradation with the kernels 4.12-rc1 and
> 4.12-rc2 in the network virtio driver. Download rate drops down to about
> 100kB/s.
>
> I bisected it and it is caused by patch
> d85b758f72b05a774045545f24d70980e3e9aac4 ("virtio_net: fix support for
> small rings"). When I revert this patch, the problem goes away.
>
> The host is Debian Jessie with kernel 4.4.62, the guest is Debian Sid with
> kernel 4.12-rc.
>
> Mikulas
Thanks for the report!
I'm not sure what causes it on this host. I'll try to reproduce.
Meanwhile, could you please locate this line of code:
+ vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
and add something like
printk(KERN_ERR, "min buf = 0x%x expected 0x%x size 0x%x big %d\n",
vi->rq[i].min_buf_len, GOOD_PACKET_LEN,
virtqueue_get_vring_size(vi->rq[i].vq),
(int)vi->big_packets);
after it?
Then boot and capture the output.
Thanks!
--
MST
^ permalink raw reply [flat|nested] 5+ messages in thread
* network performance degradation in virtio_net in 4.12-rc
@ 2017-05-22 14:25 Mikulas Patocka
0 siblings, 0 replies; 5+ messages in thread
From: Mikulas Patocka @ 2017-05-22 14:25 UTC (permalink / raw)
To: Michael S. Tsirkin, Jason Wang; +Cc: netdev, kvm, virtualization
Hi
I see severe network performance degradation with the kernels 4.12-rc1 and
4.12-rc2 in the network virtio driver. Download rate drops down to about
100kB/s.
I bisected it and it is caused by patch
d85b758f72b05a774045545f24d70980e3e9aac4 ("virtio_net: fix support for
small rings"). When I revert this patch, the problem goes away.
The host is Debian Jessie with kernel 4.4.62, the guest is Debian Sid with
kernel 4.12-rc.
Mikulas
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2017-05-22 21:50 UTC | newest]
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2017-05-22 14:25 network performance degradation in virtio_net in 4.12-rc Mikulas Patocka
2017-05-22 17:42 ` Michael S. Tsirkin
2017-05-22 21:50 ` Mikulas Patocka
2017-05-22 17:42 ` Michael S. Tsirkin
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2017-05-22 14:25 Mikulas Patocka
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