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

From: Zoltan Kiss
Date: Tue Feb 04 2014 - 14:19:12 EST

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@xxxxxxxxxx>

Sorry for the delay.

Paul, thanks for reviewing.

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>


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.


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