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

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Message-ID: <54931513.8040606@citrix.com>
Date:	Thu, 18 Dec 2014 17:55:31 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	David Miller <davem@...emloft.net>
CC:	<netdev@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
	<ian.campbell@...rix.com>, <wei.liu2@...rix.com>
Subject: Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify
 again

On 18/12/14 17:50, David Miller wrote:
> From: David Vrabel <david.vrabel@...rix.com>
> Date: Thu, 18 Dec 2014 11:13:06 +0000
> 
>> 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>
> 
> Applied, and I assume that 3.18 -stable needs this as well?

Yes, please.  Without it, netback just doesn't work with an important
use case.

Thanks.

David
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