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
