linux-kernel - Re: + clocksource-increase-initcall-priority.patch added to -mm tree

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Message-Id: <1160339986.3693.135.camel@c-67-180-230-165.hsd1.ca.comcast.net>
Date:	Sun, 08 Oct 2006 13:39:46 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	tglx@...utronix.de
Cc:	akpm@...l.org, johnstul@...ibm.com, mingo@...e.hu,
	zippel@...ux-m68k.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: + clocksource-increase-initcall-priority.patch added to -mm
	tree

On Sun, 2006-10-08 at 21:03 +0200, Thomas Gleixner wrote:
> On Sun, 2006-10-08 at 10:17 -0700, Daniel Walker wrote:
> > There was a special case inside kernel/time/clocksource.c to prevent
> > clock switching during boot up. If you remove that (which I have) then
> > you will end up with clock switching happening a few times during bootup
> > (whenever a new highest rated clock is registered), that's the churn I'm
> > referring to.
> > 
> > The churn is not optimal. I've used postcore to prevent it, and make the
> > API usable earlier. So there is a reason for the change. 
> 
> Yes, a bad one. The disabling had a totally different reason and you are
> not listening at all.

I am listening, Thomas .. 

> You just introduce a problem again, because it does not happen on your
> machines and you think, that some not yet available instrumentation code
> needs high resolution time stamps. 

Ok.

> The reason why this was delayed into late boot is simply that the
> unstable, unsynchronized TSC's made way too much trouble and the pmtimer
> can not be initialized early.
> 
> I'm not going to accept that. Your change might work on 5 machines you
> have tested on, but we start over with the same breakage we solved
> already. 

Your going to have to explain the breakage further. I don't recall
seeing any discussion on this.

> This early boot instrumentation code can work with low resolution time
> information quite well and none of the boot code does need any high res
> time information. Boot code is different from a running system and has
> different requirements. 
> 
> This is a solution for a nonexisting problem, which just brings back
> already solved ones.

There is at least one existing problem which it does solve. How about we
discuss the early TSC boot breakage, which you mention above, so I can
properly fix this situation.

Daniel

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