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

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Message-ID: <20061028194245.GA24083@hockin.org>
Date:	Sat, 28 Oct 2006 12:42:45 -0700
From:	thockin@...kin.org
To:	Willy Tarreau <w@....eu>
Cc:	Andi Kleen <ak@...e.de>, Lee Revell <rlrevell@...-job.com>,
	Luca Tettamanti <kronos.it@...il.com>,
	linux-kernel@...r.kernel.org, john stultz <johnstul@...ibm.com>
Subject: Re: AMD X2 unsynced TSC fix?

On Sat, Oct 28, 2006 at 09:32:18PM +0200, Willy Tarreau wrote:
> > Was the problem that they were not synced at poweron or that they would
> > drift due to power-states?
> 
> They resynced at power up, but would constantly drift. I don't even know
> if it was caused by power states. When the machine was loaded, a single
> task moving across the cores could see its time jump back and forth 
> several times a second by an offset sometimes close to +2/-2s.

That sounds like C1, to me.

> > Did you try running with idle=poll, to avoid ever entering C1 state (hlt)?
> 
> Yes, I remember trying such things. I also tried 'nohlt', completely
> disabling power management, including ACPI, etc... I also tried vanilla
> kernels as well as severely patched ones, but the problem remained the
> same in all circumstances, that only 'notsc' could solve.

That's exceedingly strange.  On my dual-socket dual-core, I can get
roughly synced TSCs (no appreciable drift) by just using idle=poll.  If
that did not work for you, I'd really want to poke at the system more.

> BTW, I've just found a remain of dmesg capture after boot in case you'd
> like to look for anything in it.

A dmesg won't be that useful, I'd actually have to poke at the system.
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