Re: [Xen-devel] [PATCH net-next] xen-netback: Schedule NAPI from dealloc thread instead of callback

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 13/03/14 10:42, Ian Campbell wrote:
> On Thu, 2014-03-13 at 10:17 +0000, Wei Liu wrote:
> > On Wed, Mar 12, 2014 at 09:04:41PM +0000, Zoltan Kiss wrote:
> > > If there are unconsumed requests in the ring, but there isn't enough free
> > > pending slots, the NAPI instance deschedule itself. As the frontend won't send
> > > any more interrupts in this case, it is the task of whoever release the pending
> > > slots to schedule the NAPI instance in this case. Originally it was done in the
> > > callback, but it's better at the end of the dealloc thread, otherwise there is
> > > a risk that the NAPI instance just deschedule itself as the dealloc thread
> > > couldn't release any used slot yet. However, as there are a lot of pending
> > > packets, NAPI will be scheduled again, and it is very unlikely that the dealloc
> > > thread can't release enough slots in the meantime.
> > So this patch restores the property that "only two parties access the
> > ring", right?
> I think so, and therefore:
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
I've just discussed this with Ian, this solution still doesn't solve the 
racing between NAPI and the dealloc thread, however it only causes some 
unnecessary napi_schedule's, not ring stalls.
There is a better solution, I'll post it as soon as it passes all the test!

Zoli


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