netdev - RE: [PATCH net-next v3 8/9] xen-netback: Timeout packets in RX path

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Date:	Mon, 13 Jan 2014 09:53:00 +0000
From:	Paul Durrant <Paul.Durrant@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Jonathan Davies" <Jonathan.Davies@...rix.com>
Subject: RE: [PATCH net-next v3 8/9] xen-netback: Timeout packets in RX path

> -----Original Message-----
> From: Zoltan Kiss
> Sent: 13 January 2014 00:20
> To: Paul Durrant; Ian Campbell; Wei Liu; xen-devel@...ts.xenproject.org;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org; Jonathan Davies
> Subject: Re: [PATCH net-next v3 8/9] xen-netback: Timeout packets in RX
> path
> 
> On 09/01/14 09:20, Paul Durrant wrote:
> >> We are adding the skb to vif->rx_queue even when
> >> xenvif_rx_ring_slots_available(vif, min_slots_needed) said there is no
> >> space for that. Or am I missing something? Paul?
> >>
> > That's correct. Part of the flow control improvement was to get rid of
> needless packet drops. For your purposes, you basically need to avoid using
> the queuing discipline and take packets into netback's vif->rx_queue
> regardless of the state of the shared ring so that you can drop them if they
> get beyond a certain age. So, perhaps you should never stop the netif
> queue, place an upper limit on vif->rx_queue (either packet or byte count)
> and drop when that is exceeded (i.e. mimicking pfifo or bfifo internally).
> >
> How about this:
> - when the timer fires first we wake up the thread an tell it to drop
> all the packets in rx_queue
> - start_xmit then can drain the qdisc queue into the device queue
> - additionally, the RX thread should stop that timer when it was able to
> do some work
> 

Yes, you could do it that way.

  Paul
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