netdev - Re: HTB accuracy for high speed

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Message-ID: <20090516141430.GB3013@ami.dom.local>
Date:	Sat, 16 May 2009 16:14:30 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Antonio Almeida <vexwek@...il.com>
Cc:	netdev@...r.kernel.org, kaber@...sh.net, davem@...emloft.net,
	devik@....cz
Subject: Re: HTB accuracy for high speed

On Fri, May 15, 2009 at 03:49:31PM +0100, Antonio Almeida wrote:
...
> I also note that, for HTB rate configurations over 500Mbit/s on leaf
> class, when I stop the traffic, in the output of "tc -s -d class ls
> dev eth1" command, I see that leaf's rate (in bits/s) is growing
> instead of decreasing (as expected since I've stopped the traffic).
> Rate in pps is ok and decreases until 0pps. Rate in bits/s increases
> above 1000Mbit and stays there for a few minutes. After two or three
> minutes it becomes 0bit. The same happens for it's ancestors (also for
> root class).Here's tc output of my leaf class for this situation:
> 
> class htb 1:108 parent 1:10 leaf 108: prio 7 quantum 1514 rate
> 555000Kbit ceil 555000Kbit burst 70901b/8 mpu 0b overhead 0b cburst
> 70901b/8 mpu 0b overhead 0b level 0
>  Sent 120267768144 bytes 242475339 pkt (dropped 62272599, overlimits 0
> requeues 0)
>  rate 1074Mbit 0pps backlog 0b 0p requeues 0
>  lended: 242475339 borrowed: 0 giants: 0
>  tokens: 8 ctokens: 8

This looks like a regular bug. I guess it's an overflow in
gen_estimator(), but I'm not sure there is nothing more. Could you
try the patch below? (An offset warning when patching 2.6.25 is OK)

Thanks,
Jarek P.
---

 net/core/gen_estimator.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c
index 9cc9f95..87f0ced 100644
--- a/net/core/gen_estimator.c
+++ b/net/core/gen_estimator.c
@@ -127,7 +127,11 @@ static void est_timer(unsigned long arg)
 		npackets = e->bstats->packets;
 		rate = (nbytes - e->last_bytes)<<(7 - idx);
 		e->last_bytes = nbytes;
-		e->avbps += ((long)rate - (long)e->avbps) >> e->ewma_log;
+		if (rate > e->avbps)
+			e->avbps += (rate - e->avbps) >> e->ewma_log;
+		else
+			e->avbps -= (e->avbps - rate) >> e->ewma_log;
+
 		e->rate_est->bps = (e->avbps+0xF)>>5;
 
 		rate = (npackets - e->last_packets)<<(12 - idx);
--
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