netdev - Re: [Xen-devel] [PATCH net V2] xen-netback: don't move event pointer in TX credit timeout callback

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Message-ID: <20140515135906.GH1117@zion.uk.xensource.com>
Date:	Thu, 15 May 2014 14:59:06 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>, <xen-devel@...ts.xen.org>,
	<netdev@...r.kernel.org>, Paul Durrant <paul.durrant@...rix.com>,
	<jajcus@...cus.net>
Subject: Re: [Xen-devel] [PATCH net V2] xen-netback: don't move event pointer
 in TX credit timeout callback

On Thu, May 15, 2014 at 02:40:58PM +0100, David Vrabel wrote:
> On 15/05/14 12:59, Wei Liu wrote:
> > ... otherwise the frontend will try to send TX event all the time, even
> > if no progress can be made. The pointer should only be advanced by the
> > routine that actually processes the ring (that is, xenvif_poll).
> 
> No it does not.  RING_FINAL_CHECK_FOR_REQUESTS() only advances the event
> index if the ring is empty.
> 
> This will also result in xenvif_up() failing to properly enable the event.
> 
> I think Jacek's bug may be that netback fails to call napi_complete()
> when credit is exceeded and there still outstanding requests on the
> from-guest ring and thus napi repeatedly polls.
> 

Correct. We should call napi_complete if this vif is rate limited.

Wei.
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