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

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Message-ID: <20140515181638.GG10525@zion.uk.xensource.com>
Date:	Thu, 15 May 2014 19:16:38 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>, Jacek Konieczny <jajcus@...cus.net>,
	<xen-devel@...ts.xen.org>, <netdev@...r.kernel.org>,
	Paul Durrant <paul.durrant@...rix.com>
Subject: 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:
> >On Thu, May 15, 2014 at 05:34:09PM +0100, Zoltan Kiss wrote:
> >[...]
> >>>>>
> >>>>>  		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.
> >>
> >>>
> >
> >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.
> >

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

Wei.
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