linux-kernel - Re: [PATCH] Typo in x86 apic.c with DIVISOR setup

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Date:	Fri, 10 Oct 2008 11:01:00 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Typo in x86 apic.c with DIVISOR setup


* Cyrill Gorcunov <gorcunov@...il.com> wrote:

> Ah, it was CONFG who is guilty :) This is true indeed, thanks!

yeah.

> But here is not the same
> 
>        apic_write(APIC_TDCR,
>                (tmp_value & ~(APIC_TDR_DIV_1 | APIC_TDR_DIV_TMBASE)) |
> -               APIC_TDR_DIV_16);
> +               APIC_TDR_DIV);
> 
> On x86_64 it will be 1 now but we've used 16 for a long time in 
> purpose to slowdown processor's bus CLKs from APIC point of view. So I 
> don't think it's good idea to change it now. If we start using divisor 
> 1 today -- it would work for some time 'till processor bus raised to 
> the some speed when we'll get counter underflow before calibration 
> finished.
> 
> So could you please split the patch into two:
> 1) Plain CONFG typo fix (which is completely Ack'ed)
> 2) APIC divisor patch (which I'm not sure if we've to touch)

okay, since we typoed that CONFG thing (sidenote: we really need a 
.config flag that will start a grep that fails the build if there's a 
non-existent CONFIG option anywhere in the tree), we basically tested 
the divisor of 16 on a wide range of boxes.

So .. how about just standardizing on the divisor of 16 on both 32-bit 
and 64-bit?

	Ingo
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