netdev - Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

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Message-ID: <20141218115117.GN1904@zion.uk.xensource.com>
Date:	Thu, 18 Dec 2014 11:51:18 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	<netdev@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>
Subject: Re: [PATCHv1 net] xen-netback: support frontends without
 feature-rx-notify again

On Thu, Dec 18, 2014 at 11:13:06AM +0000, David Vrabel wrote:
> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
> feature-rx-notify mandatory) incorrectly assumed that there were no
> frontends in use that did not support this feature.  But the frontend
> driver in MiniOS does not and since this is used by (qemu) stubdoms,
> these stopped working.
> 
> Netback sort of works as-is in this mode except:
> 
> - If there are no Rx requests and the internal Rx queue fills, only
>   the drain timeout will wake the thread.  The default drain timeout
>   of 10 s would give unacceptable pauses.
> 
> - If an Rx stall was detected and the internal Rx queue is drained,
>   then the Rx thread would never wake.
> 
> Handle these two cases (when feature-rx-notify is disabled) by:
> 
> - Reducing the drain timeout to 30 ms.
> 
> - Disabling Rx stall detection.
> 
> Reported-by: John <jw@...learfallout.net>
> Tested-by: John <jw@...learfallout.net>
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>

Reviewed-by: Wei Liu <wei.liu2@...rix.com>
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