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

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Message-Id: <20140109.230629.123446421132170371.davem@davemloft.net>
Date:	Thu, 09 Jan 2014 23:06:29 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	wei.liu2@...rix.com
Cc:	paul.durrant@...rix.com, netdev@...r.kernel.org,
	xen-devel@...ts.xen.org, ian.campbell@...rix.com,
	david.vrabel@...rix.com
Subject: Re: [PATCH net-next v2] xen-netback: stop vif thread spinning if
 frontend is unresponsive

From: Wei Liu <wei.liu2@...rix.com>
Date: Wed, 8 Jan 2014 19:37:16 +0000

> 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>

Applied.
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