Re: Performance regression with virtio_net

On Thu, Jul 27, 2017 at 12:09:42PM -0500, Seth Forshee wrote:

I'm seeing a performance regression with virtio_net that looks to have
started in 4.12-rc1. I only see it in one context though, downloading
snap packages from the Ubuntu snap store. For example:

 https://api.snapcraft.io/api/v1/snaps/download/b8X2psL1ryVrPt5WEmpYiqfr5emixTd7_1797.snap

which redirects to Internap's CDN. Normally this downloads in a few
seconds at ~10 MB/s, but with 4.12 and 4.13 it takes minutes with a rate
of ~150 KB/s. Everything else I've tried downloads as normal speeds.

So just wget that URL should be enough?

I bisected this to 680557cf79f8 "virtio_net: rework mergeable buffer
handling". If I revert this on top of 4.13-rc2 (along with other changes
needed to successfully revert it) speeds return to normal.

Thanks,
Seth

Interesting. A more likely suspect would be
e377fcc8486d40867c6c217077ad0fa40977e060 - could you please try
reverting that one instead?
Also, could you please look at mergeable_rx_buffer_size in sysfs with
and without the change?

-- 
MST