Re: [Xen-devel] [PATCH net-next v3 8/9] xen-netback: Timeout packets in RX path

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Zoltan Kiss
> Sent: 13 January 2014 00:20
> To: Paul Durrant; Ian Campbell; Wei Liu; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; 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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