netdev - Re: [RFC PATCH 12/12] net: sched: pfifo_fast new option to deque multiple pkts

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Message-ID: <56841EBC.3000102@gmail.com>
Date:	Wed, 30 Dec 2015 10:13:16 -0800
From:	John Fastabend <john.fastabend@...il.com>
To:	daniel@...earbox.net, eric.dumazet@...il.com, jhs@...atatu.com,
	aduyck@...antis.com, brouer@...hat.com, davem@...emloft.net
CC:	john.r.fastabend@...el.com, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 12/12] net: sched: pfifo_fast new option to deque
 multiple pkts

On 15-12-30 09:55 AM, John Fastabend wrote:
> Now that pfifo_fast is using the alf_queue data structures we can
> dequeue multiple skbs and save some overhead.
> 
> This works because the bulk dequeue logic accepts skb lists already.
> 
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> ---

oops I didn't mean to send this it obviously doesn't work because
until you have 8 skbs nothing gets dequeued. This was just a test
patch I was looking at for perf numbers. Maybe it provides some
insight into how we could build a pfifo_bulk or add an option to
pfifo_fast to dequeue multiple pkts at a time. The trick is to
sort out how long to wait for packets to build up or possibly
just remove this line,

+	if (this_cpu_ptr(qdisc->cpu_qstats)->qlen < 8)
+		return NULL;

And opportunistically pull packets out at the risk of over-running
the driver if those are large skbs.

.John
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