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

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Date:	Sat, 28 Oct 2006 13:11:14 -0700
From:	Andi Kleen <ak@...e.de>
To:	Willy Tarreau <w@....eu>
Cc:	Lee Revell <rlrevell@...-job.com>, thockin@...kin.org,
	Luca Tettamanti <kronos.it@...il.com>,
	linux-kernel@...r.kernel.org, john stultz <johnstul@...ibm.com>
Subject: Re: AMD X2 unsynced TSC fix?

On Saturday 28 October 2006 13:04, Willy Tarreau wrote:

> I really think that the hardware was doing tricks far beyond my knowledge,
> because on another Sun (a V40Z), there were 4 dual cores which I never saw
> out of sync even after hours of testing. But the HPET was available in it,
> I don't remember if it's used by default when detected.

I think some system occasionally ramp the clock for thermal management,
but that should be rare.

> No I did not "force" anything at first. You take the RHEL3 CD, you install
> it, reboot and watch your logs report negative times, then scratch your
> head, first call red hat dumb ass, and after a few tests, apologize to the
> poor innocent red hat 

Well they should have fixed the kernel to fall back to another clock
by backporting the appropiate fixes from mainline. I assume they
did actually.

> and call the box a total crap. To put it shortly 
> (might be useful for people who Google for it) : Dual-core Sun x2100 is
> unreliable out of the box under Linux.

No that shouldn't be true with any modern kernel. It will just fallback
to HPET or more likely PMtimer.

>
> > In the default configuration there shouldn't be any problems
> > like this, it will just run slower because the kernel falls back to a
> > slower time source.
>
> You have to specify "notsc" for this.

No, the kernel should work out of the box. Some older kernels didn't
at various points of time though.

-Andi
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