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

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Date:	Mon, 2 Feb 2009 20:21:55 +0200
From:	Denys Fedoryschenko <denys@...p.net.lb>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] [RESEND] iproute2 : invalid burst/cburst calculation with hrtimers

Why floating point?
It seems get_hz (and burst in result) just cannot be too low.
Still seems some code in HTB rely on jiffies, so get_hz() probably just wrong.

Already i'm tried to increase burst/cburst calculation precision, but it will 
fail still with such high get_hz variable.

Ii dont know way to get real HZ variable from userspace.

Here is Martin Devera answer
>but it really
>seems as if get_hz() is too high.
>For 1000Mbps - it is 1MB per 1 ms and assuming HZ=1000, then burst
>should be about 1MB.
>But I must admit, I'm not familiar with latest state of HZ in kernel.
>There was "NO_NZ" effort IIRC, where the HZ granularity can be
>considerably finer - but still not infinite.



On Monday 02 February 2009 20:07:42 Stephen Hemminger wrote:
> On Mon, 2 Feb 2009 19:26:17 +0200
>
> Denys Fedoryschenko <denys@...p.net.lb> wrote:
> > ------------->
> > iproute2 : invalid burst/cburst calculation with hrtimers
> >
> > If hrtimers on, /proc/net/psched shows 4th variable
> > as 1000000000
> > Because burst calculated by division rate to this variable,
> > it will be almost always zero. As result, we will get higher system
> > load on low rates, and on high rates shaper will not able to process
> > data. So it is kind of critical bugfix for systems with hrtimers.
> > It is checked and proved. Core 2 Quad was not able to
> > shape 200Mbps, and gave only 180-190. It is more safe to set it
> > to 1000HZ. If user wants, he can set custom "env" HZ variable.
> >
> > Signed-off-by: Denys Fedoryschenko <denys@...p.net.lb>
> > ---
> >
> > -------------------------------------------------------
>
> I would rather this be converted to floating point.


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