linux-kernel - Re: [RFC patch] reset TSC at the begining of check_tsc

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Message-ID: <87my8rcbp7.fsf@basil.nowhere.org>
Date:	Tue, 02 Jun 2009 09:54:44 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Luming Yu <luming.yu@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC patch] reset TSC at the begining of check_tsc_warp

Luming Yu <luming.yu@...il.com> writes:

> Hello,
>
> Without this patch, we always get kernel warning that TSC warp between CPUs,
> and TSC is marked unstable due to check_tsc_sync_source failed if the CPUs
> have the problem of not-synced initial TSC.
>
> It hurts CPUs with constant-tsc feature, but with unsynced initial TSC value...
>
> The downside is we could break perfect synced TSC with this patch.

s/could/will definitely/

So you're hurting the good systems for one buggy box. I don't think
that's a good idea.

Possible alternatives:
- black list that system with DMI
- try to detect it by checking constant_tsc and still unsynchronized TSC
- just give up and say the system won't be able to use TSC unless the BIOS
fixes its act.

The third option is probably not the worst.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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