linux-kernel - Re: cpufreq affects traffic control rates

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Date:	Wed, 29 Aug 2007 10:20:05 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
Cc:	DervishD <lkml@...vishd.net>,
	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: cpufreq affects traffic control rates

On Wed, 29 Aug 2007 17:26:24 +0200 (CEST)
Jan Engelhardt <jengelh@...putergmbh.de> wrote:

> 
> On Aug 28 2007 15:23, Stephen Hemminger wrote:
> >>     I noticed lately that my traffic control rates were being very slow,
> >> about 40% less than expected, and finally spotted the problem: cpufreq.
> >> 
> >>     Looks like HTB puts buckets according to the requested rate but
> >> assuming that the CPU is running at its default clock or something like
> >> that.
> >> 
> >Is the problem configuration of network scheduler clock? In 2.6.20 and earlier, you
> >could use CPU cycle counter (later kernels only use time of day).  So try
> >switching to jiffies or gettimeofday.
> 
> This should not have been removed. CPUs with constant_tsc
> could still be used with "CPU cycle counter" method.
> 
> 
> 	Jan

It was removed because the core clock subsystem now manages the choice
of CPU clock correctly and should provide the highest resolution possible
on the hardware.

Plus a whole bunch of grotty macro code gets removed. And the math
handling was more standard/simpler.

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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