RE: [Xen-devel] [RFC PATCH 3/6] netback: switch to NAPI + kthread model

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Ian Campbell
> Sent: 16 January 2012 10:45
> To: Wei Liu (Intern)
> Cc: netdev@xxxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx; David Vrabel;
> konrad.wilk@xxxxxxxxxx
> Subject: Re: [Xen-devel] [RFC PATCH 3/6] netback: switch to NAPI + kthread
> model
> 
> On Mon, 2012-01-16 at 09:33 +0000, Wei Liu (Intern) wrote:
> > On Fri, 2012-01-13 at 18:21 +0000, David Vrabel wrote:
> > > On 13/01/12 16:59, Wei Liu wrote:
> > > > This patch implements 1:1 model netback. We utilizes NAPI and
> > > > kthread to do the weight-lifting job:
> > > >
> > > >   - NAPI is used for guest side TX (host side RX)
> > > >   - kthread is used for guest side RX (host side TX)
> > > >
> > > > This model provides better scheduling fairness among vifs. It also
> > > > lays the foundation for future work.
> > > >
> > > > The major defect for the current implementation is that in the
> > > > NAPI poll handler we don't actually disable interrupt. Xen stuff
> > > > is different from real hardware, it requires some other tuning of
> > > > ring macros.
> > >
> > > RING_FINAL_CHECK_FOR_REQUESTS() looks it does the correct thing to
> me.
> > >
> > > David
> >
> > I need to stop the other end from generating events, so
> > RING_FINAL_CHECK_FOR_REQUESTS is not the right answer I think.
> 
> What you need is a variant which sets req_event some large distance into
> the future instead of to just req_cons + 1. Or possibly it should be set to just
> in the past (e.g. req_cons - 1). Call it something like
> RING_POLL_FOR_REQUESTS().
> 

Can you just simply avoid calling RING_FINAL_CHECK_FOR_REQUESTS() unless you actually want to re-enable 'interrupts'? All it does is manipulate the event pointer and tell you whether there are still unconsumed requests.

  Paul
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