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

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Message-ID: <1326710711.17210.411.camel@zakaz.uk.xensource.com>
Date:	Mon, 16 Jan 2012 10:45:11 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	"Wei Liu (Intern)" <wei.liu2@...rix.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
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().

Ian.

> 
> 
> Wei.
> 


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