netdev - Re: [kvm-devel] [PATCH resent] virtio_net: Fix stalled inbound trafficon early packets

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Message-Id: <200712131930.31602.borntraeger@de.ibm.com>
Date:	Thu, 13 Dec 2007 19:30:31 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	dor.laor@...ranet.com
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [kvm-devel] [PATCH resent] virtio_net: Fix stalled inbound trafficon early packets

Am Donnerstag, 13. Dezember 2007 schrieb Dor Laor:
> You're right I got confused somehow.
> So in that case setting the driver status field on open in addition to 
> your enable will do the trick.
> On DRIVER_OPEN the host will trigger an interrupt if the queue is not 
> empty..
> Thanks,
> Dor

After looking into some other drivers, I prefer my first patch (moving 
napi_enable) ;-)

There are some drivers like xen-netfront, b44, which call napi_enable before 
the buffers are passed to the hardware. So it seems that moving napi is 
also a valid option.

But maybe I can just wait until Rusty returns from vacation (I will leave 
next week) so everything might be wonderful when I return ;-)

Rusty, if you decide to apply my patch, there is one downside: The debugging 
code in virtio_ring sometimes triggers with a false positive:

try_fill_recv calls vring_kick. Here we do a notify to the host. This might 
cause an immediate interrupt, triggering the poll routine before vring_kick 
can run END_USE. This is no real problem, as we dont touch the vq after 
notify.

Christian, facing 64 guest cpus unconvering all kind of races

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