netdev - Re: HTB accuracy for high speed

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Message-Id: <20090518.145233.212710505.davem@davemloft.net>
Date:	Mon, 18 May 2009 14:52:33 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jarkao2@...il.com
Cc:	dada1@...mosbay.com, vexwek@...il.com, netdev@...r.kernel.org,
	kaber@...sh.net, devik@....cz
Subject: Re: HTB accuracy for high speed

From: Jarek Poplawski <jarkao2@...il.com>
Date: Mon, 18 May 2009 19:23:49 +0200

> On Mon, May 18, 2009 at 06:40:56PM +0200, Eric Dumazet wrote:
>> With a typical estimator "1sec 8sec", ewma_log value is 3
>> 
>> At gigabit speeds, we are very close to overflow yes, since
>> we only have 27 bits available, so 134217728 bytes per second
>> or 1073741824 bits per second.
>> 
>> So formula :
>> e->avbps += ((long)rate - (long)e->avbps) >> e->ewma_log;
>> is going to overflow.
>> 
>> One way to avoid the overflow would be to use a smaller estimator, like "500ms 4sec" 
>> 
>> Or use a 64bits rate & avbps, this is needed fo 10Gb speeds I suppose...
> 
> Yes, I considered this too, but because of an overhead I decided to
> fix as designed (according to the comment) for now. But probably you
> are right, and we should go further, so I'm OK with your patch.

I like this patch too, Eric can you submit this formally with
proper signoffs etc.?

Thanks!
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