netdev - Re: [PATCH] net_sched: accurate bytes/packets stats/rates

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Date:	Sun, 16 Jan 2011 23:35:40 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>, jamal <hadi@...erus.ca>
Subject: Re: [PATCH] net_sched: accurate bytes/packets stats/rates

On Fri, Jan 14, 2011 at 11:03:42AM -0800, Stephen Hemminger wrote:
> From Eric Dumazet <eric.dumazet@...il.com>
> 
> In commit 44b8288308ac9d (net_sched: pfifo_head_drop problem), we fixed
> a problem with pfifo_head drops that incorrectly decreased
> sch->bstats.bytes and sch->bstats.packets
> 
> Several qdiscs (CHOKe, SFQ, pfifo_head, ...) are able to drop a
> previously enqueued packet, and bstats cannot be changed, so
> bstats/rates are not accurate (over estimated)
> 
> This patch changes the qdisc_bstats updates to be done at dequeue() time
> instead of enqueue() time. bstats counters no longer account for dropped
> frames, and rates are more correct, since enqueue() bursts dont have
> effect on dequeue() rate.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> Acked-by: Stephen Hemminger <shemminger@...tta.com>
> 
> CC: Patrick McHardy <kaber@...sh.net>
> CC: Jarek Poplawski <jarkao2@...il.com>
> CC: jamal <hadi@...erus.ca>
...
> --- a/net/sched/sch_drr.c	2011-01-14 09:19:00.830857886 -0800
> +++ b/net/sched/sch_drr.c	2011-01-14 09:28:20.398631228 -0800
> @@ -376,7 +376,6 @@ static int drr_enqueue(struct sk_buff *s
>  	}
>  
>  	bstats_update(&cl->bstats, skb);

Why leave leaf classes with different stats?

Jarek P.

> -	qdisc_bstats_update(sch, skb);
>  
>  	sch->q.qlen++;
>  	return err;
...
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