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

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Date:	Mon, 17 Jan 2011 08:09:40 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	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 Mon, Jan 17, 2011 at 6:35 AM, Jarek Poplawski <jarkao2@...il.com> wrote:
> 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?
>

HTB also has the same problem, and I have fixed in my own product, but
the patch was rejected.

http://patchwork.ozlabs.org/patch/6227/

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



-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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