netdev - RE: [PATCH net] xen-netback: fix abuse of napi budget

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Date:	Tue, 10 Dec 2013 10:48:13 +0000
From:	Paul Durrant <Paul.Durrant@...rix.com>
To:	Wei Liu <wei.liu2@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>
CC:	Ian Campbell <Ian.Campbell@...rix.com>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Wei Liu <wei.liu2@...rix.com>
Subject: RE: [PATCH net] xen-netback: fix abuse of napi budget

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@...rix.com]
> Sent: 10 December 2013 10:45
> To: David Vrabel
> Cc: Ian Campbell; Paul Durrant; xen-devel@...ts.xen.org;
> netdev@...r.kernel.org; Wei Liu
> Subject: Re: [PATCH net] xen-netback: fix abuse of napi budget
> 
> On Tue, Dec 10, 2013 at 10:37:36AM +0000, Wei Liu wrote:
> > On Tue, Dec 10, 2013 at 10:30:13AM +0000, David Vrabel wrote:
> > > On 10/12/13 10:25, Ian Campbell wrote:
> > > > On Tue, 2013-12-10 at 10:16 +0000, Paul Durrant wrote:
> > > >> netback seemed to be somewhat confused about the napi budget
> parameter and
> > > >> basically ignored it. This patch fixes that, properly limiting the work
> done
> > > >> in each poll.
> > > >
> > > > What do you mean "ignored", xenvif_tx_submit seems to be tracking
> and
> > > > testing work_done against the budget.
> > >
> > > I have seen this warning in net_rx_action() trigger.
> > >
> > > 	WARN_ON_ONCE(work > weight);
> > >
> > > Which means netback wasn't limiting the work done.
> > >
> >
> > But in the original code work_done is returned by xenvif_tx_submit which
> > has guard against that situation, right?
> >
> 
> And now I think I spot a bug...
> 
>   work_done = xenvif_tx_submit(vif, nr_gops);
> 
> The second argument should really be "budget". :-(
> 

Yep - that's basically the problem.

  Paul

> Wei.
> 
> > Wei.
> >
> > > David
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