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

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Message-ID: <20140515135824.GG1117@zion.uk.xensource.com>
Date:	Thu, 15 May 2014 14:58:24 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	Jacek Konieczny <jajcus@...cus.net>
CC:	Wei Liu <wei.liu2@...rix.com>, <xen-devel@...ts.xen.org>,
	<netdev@...r.kernel.org>, Paul Durrant <paul.durrant@...rix.com>
Subject: Re: [PATCH net V2] xen-netback: don't move event pointer in TX
 credit timeout callback

On Thu, May 15, 2014 at 03:04:36PM +0200, Jacek Konieczny wrote:
> On 05/15/14 13:59, 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).
> > 
> > Reported-by: Jacek Konieczny <jajcus@...cus.net>
> > Signed-off-by: Wei Liu <wei.liu2@...rix.com>
> > Acked-by: Ian Campbell <ian.campbell@...rix.com>
> > Cc: Paul Durrant <paul.durrant@...rix.com>
> > ---
> >  drivers/net/xen-netback/netback.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> > index 7666540..8e2cbeb 100644
> > --- a/drivers/net/xen-netback/netback.c
> > +++ b/drivers/net/xen-netback/netback.c
> > @@ -658,7 +658,7 @@ void xenvif_check_rx_xenvif(struct xenvif *vif)
> >  {
> >  	int more_to_do;
> >  
> > -	RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do);
> > +	more_to_do = RING_HAS_UNCONSUMED_REQUESTS(&vif->tx);
> > 
> 
> Unfortunately, this seems not enough to fix the problem I have reported
> here:
> http://lists.xenproject.org/archives/html/xen-devel/2014-05/msg01183.html
> 
> The dom0 network still stalls when using rate limiting on a VIF
> interface after applying this patch to my 3.14.3 kernel (100% CPU#1
> usage in the 'soft interrupts').
> 

Oh I was looking at the aggregated stats that's why the number looked
normal to me. :-/

> Greets,
> 	Jacek
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