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

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Message-ID: <20140120163814.GE11681@zion.uk.xensource.com>
Date:	Mon, 20 Jan 2014 16:38:14 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	<ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
Subject: Re: [PATCH net-next v2] xen-netback: Rework rx_work_todo

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>

Wei.
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