Subject: Re: [PATCH net-next v2] xen-netback: Rework rx_work_todo

From: Zoltan Kiss <[email-masked]>
Date: Tue, 4 Feb 2014 19:19:00 +0000

On 20/01/14 16:38, Wei Liu wrote:
> On Wed, Jan 15, 2014 at 05:11:07PM +0000, Zoltan Kiss wrote:
>> The recent patch to fix receive side flow control (11b57f) solved the spinning
>> thread problem, however caused an another one. The receive side can stall, if:
>> - [THREAD] xenvif_rx_action sets rx_queue_stopped to true
>> - [INTERRUPT] interrupt happens, and sets rx_event to true
>> - [THREAD] then xenvif_kthread sets rx_event to false
>> - [THREAD] rx_work_todo doesn't return true anymore
>>
>> Also, if interrupt sent but there is still no room in the ring, it take quite a
>> long time until xenvif_rx_action realize it. This patch ditch that two variable,
>> and rework rx_work_todo. If the thread finds it can't fit more skb's into the
>> ring, it saves the last slot estimation into rx_last_skb_slots, otherwise it's
>> kept as 0. Then rx_work_todo will check if:
>> - there is something to send to the ring (like before)
>> - there is space for the topmost packet in the queue
>>
>> I think that's more natural and optimal thing to test than two bool which are
>> set somewhere else.
>>
>> Signed-off-by: Zoltan Kiss <[email-masked]>
>
> Sorry for the delay.
>
> Paul, thanks for reviewing.
>
> Acked-by: Wei Liu <[email-masked]>

Hi,

This patch haven't made it to net-next yet, maybe because the subject 
doesn't suggest that this is a bugfix. I suggest to apply it as soon as 
possible, otherwise netback will be quite broken.

Zoli