netdev - Re: [PATCH] [RESEND] iproute2 : invalid burst/cburst calculation with hrtimers

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Date:	Thu, 5 Feb 2009 11:01:35 +0200
From:	Denys Fedoryschenko <denys@...p.net.lb>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Stephen Hemminger <shemminger@...ux-foundation.org>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] [RESEND] iproute2 : invalid burst/cburst calculation with hrtimers

Well, i don't know well what's wrong, but:

I have enough powerful router, 2x Quad Core 2 - 2.8 Ghz
4 x e1000e

And if i just try to shape interface for 200 Mbps with default iproute2 from 
git (and latest stable release same situation), i am getting too low 
burst/cburst. Sometimes it is even miscalculated (it can become 1500 byte, 
sometimes, while 1600 is minimum) , because yes, Stephen right, it needs 
float.
BUT.
Even i set manually twice more burst/cburst, it is just not enough for 200 
Mbps. I am checking on Cisco, rate is reaching max 180-185Mbps, and even on 
this rate buffering in qdiscs and as result jittering hard.
So this 100 bytes, which probably missing, really doesn't matter.

With 1000 HZ i have
class htb 1:10 parent 1:2 rate 220000Kbit ceil 220000Kbit burst 29067b cburst 
29067b
 Sent 14027734219153 bytes 590886842 pkt (dropped 0, overlimits 0 requeues 0)
 rate 122452Kbit 17131pps backlog 0b 0p requeues 0
 lended: 171333348 borrowed: 0 giants: 0
 tokens: 980 ctokens: 980

And it works quite well and precise.

P.S. Maybe a case, when some guy was not able to reach his gigabit with HTB 
shaper, i remember there was flowing some discussing, was somehow similar as 
my case.

On Thursday 05 February 2009 09:38:32 Jarek Poplawski wrote:
>
> I think HZ doesn't matter much in this place, because if it's ever
> triggered there is something really wrong and precision is lost.
> Anyway, this place was changed a bit in net-next.
>
> I guess I could misunderstand your previous question. If you mean this
> previous thread, then yes, IMHO CONFIG_HZ should matter for precision
> (especially places where similar loops use all such jiffies in "normal"
> situations). On the other hand, maybe I'm wrong, but using HZ 1000
> with HIGH_RES_TIMERS looks quite obvious to me...
>
> Jarek P.
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