Re: [PATCH net V2] xen-netback: don't move event pointer in TX credit timeout callback

On Thu, May 15, 2014 at 06:03:14PM +0100, Zoltan Kiss wrote:

On 15/05/14 17:53, Wei Liu wrote:

quoted

On Thu, May 15, 2014 at 05:34:09PM +0100, Zoltan Kiss wrote:
[...]

quoted

quoted

quoted

quoted

 		RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do);
-		if (!more_to_do)
+		if (!more_to_do || rate_limited)

How about calling timer_pending(&vif->credit_timeout) instead?

timer_pending(&vif->credit_timeout) covers only one of two senarios of
"credit exceeded", see tx_credit_exceeded.

The other scenario is when the packet size exceeds the credit. There is no
packet here actually, we just want to know if this vif ran out of credit and
waiting for the timer to fire.

quoted

Which place are you referring to? There's packet in the ring, right? So
you're saying in xenvif_poll "more_to_do" is true and "timer_pending" is
also true when we come to xenvif_poll again?

The goal of this patch to deschedule NAPI if the vif ran out of credit.
Either you can carry that information from build_gops via a bool, or you can
check whether the timer is pending. That's what tx_credit_exceeded does as
well, and then it checks if the actual packet fits in. But in xenvif_poll
you don't want to know whether an actual packet fits in, you only need the
information whether tx_credit_exceeded started the timer or not.
If it is, you can be sure there is no more credit. If not, you can keep the
instance running.

quoted

OK, you convinced me. I will try to rework this patch with your
approach.

Wei.