netdev - Re: qstats update in packet scheduling

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Date:	Mon, 24 Nov 2014 12:21:59 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Josh Clark <jcinma@...il.com>
Cc:	Dave Taht <dave.taht@...il.com>, netdev <netdev@...r.kernel.org>
Subject: Re: qstats update in packet scheduling

On Mon, 2014-11-24 at 14:14 -0500, Josh Clark wrote:

> At the moment, I'm using standard RED (from /net/sched/sch_red.c) with
> some printks to output qstats.

printk are slowing down the kernel and might interfere with normal
behavior. Don't use them.


> Are you saying that when I set this up, I need to use the -s flag in
> tc to maintain those statistics?

stats are maintained by the kernel no matter what.

tc -s qdisc   actually display them.

For instance, red_dump() copies the backlog from child qdisc.

static int red_dump(struct Qdisc *sch, struct sk_buff *skb)
{
...
	sch->qstats.backlog = q->qdisc->qstats.backlog;
...
}



This backlog is probably not 0 !


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