netdev - Re: [PATCH net-next v2] xen-netback: stop vif thread spinning if frontend is unresponsive

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Date:	Wed, 8 Jan 2014 19:37:16 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Paul Durrant <paul.durrant@...rix.com>
CC:	<netdev@...r.kernel.org>, <xen-devel@...ts.xen.org>,
	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [PATCH net-next v2] xen-netback: stop vif thread spinning if
 frontend is unresponsive

On Wed, Jan 08, 2014 at 12:41:58PM +0000, Paul Durrant wrote:
> The recent patch to improve guest receive side flow control (ca2f09f2) had a
> slight flaw in the wait condition for the vif thread in that any remaining
> skbs in the guest receive side netback internal queue would prevent the
> thread from sleeping. An unresponsive frontend can lead to a permanently
> non-empty internal queue and thus the thread will spin. In this case the
> thread should really sleep until the frontend becomes responsive again.
> 
> This patch adds an extra flag to the vif which is set if the shared ring
> is full and cleared when skbs are drained into the shared ring. Thus,
> if the thread runs, finds the shared ring full and can make no progress the
> flag remains set. If the flag remains set then the thread will sleep,
> regardless of a non-empty queue, until the next event from the frontend.
> 
> Signed-off-by: Paul Durrant <paul.durrant@...rix.com>
> Cc: Wei Liu <wei.liu2@...rix.com>
> Cc: Ian Campbell <ian.campbell@...rix.com>
> Cc: David Vrabel <david.vrabel@...rix.com>

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

Thanks
Wei.
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