linux-kernel - Re: [patch] x86: unify/rewrite SMP TSC sync code

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Date:	Fri, 24 Nov 2006 18:13:13 +0100
From:	Andi Kleen <ak@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...l.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch] x86: unify/rewrite SMP TSC sync code


> make the TSC synchronization code more robust, and unify it between 
> x86_64 and i386.
> 
> The biggest change is the removal of the 'fix up TSCs' code on x86_64 
> and i386, in some rare cases it was /causing/ time-warps on SMP systems.

On x86-64 I don't think it can since it doesn't check anymore on sync Intel.

> The new code only checks for TSC asynchronity - and if it can prove a 
> time-warp (if it can observe the TSC going backwards when going from one 
> CPU to another within a critical section), then the TSC clock-source is 
> turned off.

The trouble is that people are using the RDTSC anyways even if the
kernel doesn't. So some synchronization is probably a good idea.

-Andi
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