linux-kernel - Re: [PATCH net-next v2] xen-netback: Rework rx_work

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Message-ID: <52F13D24.5090405@citrix.com>
Date:	Tue, 4 Feb 2014 19:19:00 +0000
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	<ian.campbell@...rix.com>, <xen-devel@...ts.xenproject.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<jonathan.davies@...rix.com>, David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next v2] xen-netback: Rework rx_work_todo

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 <zoltan.kiss@...rix.com>
>
> Sorry for the delay.
>
> Paul, thanks for reviewing.
>
> Acked-by: Wei Liu <wei.liu2@...rix.com>

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

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