netdev - Re: [PATCH net-next v4 2/2] virtio-net: add cond

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Date: Thu, 27 Jul 2023 05:46:45 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Maxime Coquelin <maxime.coquelin@...hat.com>,
	Shannon Nelson <shannon.nelson@....com>, xuanzhuo@...ux.alibaba.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, davem@...emloft.net
Subject: Re: [PATCH net-next v4 2/2] virtio-net: add cond_resched() to the
 command waiting loop

On Thu, Jul 27, 2023 at 04:59:33PM +0800, Jason Wang wrote:
> > They really shouldn't - any NIC that takes forever to
> > program will create issues in the networking stack.
> 
> Unfortunately, it's not rare as the device/cvq could be implemented
> via firmware or software.

Currently that mean one either has sane firmware with a scheduler that
can meet deadlines, or loses ability to report errors back.

> > But if they do they can always set this flag too.
> 
> This may have false negatives and may confuse the management.
> 
> Maybe we can extend the networking core to allow some device specific
> configurations to be done with device specific lock without rtnl. For
> example, split the set_channels to
> 
> pre_set_channels
> set_channels
> post_set_channels
> 
> The device specific part could be done in pre and post without a rtnl lock?
> 
> Thanks


Would the benefit be that errors can be reported to userspace then?
Then maybe.  I think you will have to show how this works for at least
one card besides virtio.


-- 
MST