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

From: Jacek Konieczny <[email-masked]>
Date: Thu, 15 May 2014 15:04:36 +0200

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 <[email-masked]>
> Signed-off-by: Wei Liu <[email-masked]>
> Acked-by: Ian Campbell <[email-masked]>
> Cc: Paul Durrant <[email-masked]>
> ---
>  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').

Greets,
	Jacek