linux-kernel - Re: [PATCH] Fix booting pentium+ with dodgy TSC

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Message-Id: <200804070629.07704.rusty@rustcorp.com.au>
Date:	Mon, 7 Apr 2008 06:29:07 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, "H. Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org, lguest <lguest@...abs.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Fix booting pentium+ with dodgy TSC

On Sunday 06 April 2008 21:22:08 Ingo Molnar wrote:
> * Rusty Russell <rusty@...tcorp.com.au> wrote:
> > Linus please apply.  Almost by definition this patch can't make things
> > worse.
>
> well, while i agree with the patch it could make things worse. In this
> case it can cause code that has been compiled to rely on TSC to
> malfunction. For if sched_clock() was using cpu_has_tsc it could return
> 0 all the time, breaking the scheduler without the user having a clear
> idea why it broke. It isnt, and sched_clock() will work fine, but still,
> your "this cant make things worse" statement is not completely correct.

Hence the "almost".  It can't break machines, but it could make the problem 
harder to diagnose.  Given that it will unbreak at least one machine, I'm 
reasonably confident it's a win :)

>  Acked-by: Ingo Molnar <mingo@...e.hu>

Thanks!
Rusty.
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