linux-kernel - Re: AMD X2 unsynced TSC fix?

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Date:	Fri, 27 Oct 2006 20:17:35 -0400
From:	Lee Revell <rlrevell@...-job.com>
To:	Luca Tettamanti <kronos.it@...il.com>
Cc:	"thockin@...kin.org" <thockin@...kin.org>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>,
	john stultz <johnstul@...ibm.com>
Subject: Re: AMD X2 unsynced TSC fix?

On Sat, 2006-10-28 at 02:00 +0200, Luca Tettamanti wrote:
> 
> As you say you cannot use it to do timing unless you disable any power
> management on the CPU. Otherwise you can count the elapsed ticks but
> you cannot convert the number to anything meaningful.
> You may be able to emulate rdtsc for userspace but then again the
> whole point of using rdtsc is that it should be uber-fast... if rdtsc
> is emulated then you can just use gettimeofday (which is also
> optimized to be *very* fast). No? 

gettimeofday() cannot be fast if it has to use the ACPI PM timer.  It's
50% slower on my shiny new "AMD Athlon(tm)64 X2 Dual Core Processor
3800+" than on my 600Mhz Via C3, which in general is about a 10x slower
machine.  That's a massive regression.

Lee

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