linux-kernel - Re: [RFC PATCH] x86:Use cpu_khz for loops_per

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Date:	Mon, 09 Jun 2008 10:55:16 -0700
From:	Alok Kataria <akataria@...are.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Daniel Hecht <dhecht@...are.com>, Tim Mann <mann@...are.com>,
	Zach Amsden <zach@...are.com>, Sahil Rihan <srihan@...are.com>
Subject: Re: [RFC PATCH] x86:Use cpu_khz for loops_per_jiffy calculation

On Mon, 2008-06-09 at 06:11 -0700, Ingo Molnar wrote:
> * Alok Kataria <akataria@...are.com> wrote:
> 
> > --- linux-2.6.orig/arch/x86/kernel/tsc_32.c   2008-05-27 12:28:16.000000000 -0700
> > +++ linux-2.6/arch/x86/kernel/tsc_32.c        2008-06-03 17:28:46.000000000 -0700
> > @@ -401,6 +401,7 @@
> >  void __init tsc_init(void)
> >  {
> >       int cpu;
> > +     u64 lpj;
> >
> >       if (!cpu_has_tsc || tsc_disabled) {
> >               /* Disable the TSC in case of !cpu_has_tsc */
> > @@ -421,6 +422,10 @@
> >               return;
> >       }
> >
> > +     lpj = ((u64)cpu_khz * 1000);
> > +     do_div(lpj, HZ);
> > +     lpj_tsc = lpj;
> 
> that wont work very well as lpj_tsc is not declared.

lpj_tsc is declared in include/linux/delay.h, and that declaration is
available in tsc_32.c 

I compile tested against current git too and seems fine to me. 

Also this patch is not to be applied to any tree yet, i will make a
different patch which calculates lpj_tsc from tsc_khz instead and use it
only for the boor processor. 
There were some concerns from Arjan and Pavel regarding cpu frequency
being different on different cpus. I was waiting to hear back from them
before sending a new patch.

Let me know your comments on my questions/suggestions from the earlier
post
http://marc.info/?l=linux-kernel&m=121269125317375&w=2


Thanks,
Alok


> 
>         Ingo

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