netdev - Re: [PATCH net-next] virtio-net: invoke zerocopy callback on xmit path if no tx napi

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Date:   Tue, 29 Aug 2017 23:40:49 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Koichiro Den <den@...ipeden.com>, Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] virtio-net: invoke zerocopy callback on xmit
 path if no tx napi

On Tue, Aug 29, 2017 at 03:53:08PM -0400, Willem de Bruijn wrote:
> On Tue, Aug 29, 2017 at 3:42 PM, Michael S. Tsirkin <mst@...hat.com> wrote:
> > On Tue, Aug 29, 2017 at 03:35:38PM -0400, Willem de Bruijn wrote:
> >> By the way, I have had an unrelated patch outstanding for a while
> >> to have virtio-net support the VIRTIO_CONFIG_S_NEEDS_RESET
> >> command. Will send that as RFC.
> >
> > Oh nice.
> 
> Great :)
> 
> > One needs to be careful about locking there which is why
> > no devices support that yet.
> 
> I originally wrote it based on the virtnet_reset function introduced
> for xdp. Calling this from virtnet_config_changed_work is non trivial,
> as virtnet_freeze_down waits until no config worker is running.
> 
> Otherwise, I could not find any constraints on when freeze may be
> called, and it largely follows the same path. I hope I didn't miss anything.

The issue is that on freeze processes are not running so we
generally know no new packets will arrive (might be wrong
for bridging, then it's a bug). On device error you must
prevent new skbs from coming in, etc.

-- 
MST