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

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Message-ID: <20131210104443.GK32155@zion.uk.xensource.com>
Date:	Tue, 10 Dec 2013 10:44:43 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Ian Campbell <Ian.Campbell@...rix.com>,
	Paul Durrant <paul.durrant@...rix.com>,
	<xen-devel@...ts.xen.org>, <netdev@...r.kernel.org>,
	Wei Liu <wei.liu2@...rix.com>
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". :-(

Wei.

> Wei.
> 
> > David
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