netdev - Re: [PATCH iproute2] Re: HTB accuracy for high speed

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Date:	Tue, 02 Jun 2009 23:50:42 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
CC:	Antonio Almeida <vexwek@...il.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	netdev@...r.kernel.org, davem@...emloft.net, devik@....cz,
	Eric Dumazet <dada1@...mosbay.com>,
	Vladimir Ivashchenko <hazard@...ncoudi.com>
Subject: Re: [PATCH iproute2] Re: HTB accuracy for high speed

Jarek Poplawski wrote, On 06/02/2009 11:37 PM:
...

> I described the reasoning here:
> http://permalink.gmane.org/gmane.linux.network/128189

The link is stuck now, so here is a quote:

Jarek Poplawski wrote, On 05/17/2009 10:15 PM:

> Here is some additional explanation. It looks like these rates above
> 500Mbit hit the design limits of packet scheduling. Currently used
> internal resolution PSCHED_TICKS_PER_SEC is 1,000,000. 550Mbit rate
> with 800byte packets means 550M/8/800 = 85938 packets/s, so on average
> 1000000/85938 = 11.6 ticks per packet. Accounting only 11 ticks means
> we leave 0.6*85938 = 51563 ticks per second, letting for additional
> sending of 51563/11 = 4687 packets/s or 4687*800*8 = 30Mbit. Of course
> it could be worse (0.9 tick/packet lost) depending on packet sizes vs.
> rates, and the effect rises for higher rates.


Jarek P.
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