linux-kernel - Re: REGRESSION: the new i386 timer code fails to sync CPUs

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Message-Id: <20060730135518.f16c0399.akpm@osdl.org>
Date:	Sun, 30 Jul 2006 13:55:18 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Andi Kleen <ak@....de>
Cc:	johnstul@...ibm.com, smurf@...rf.noris.de,
	linux-kernel@...r.kernel.org, torvalds@...l.org, bunk@...sta.de,
	lethal@...ux-sh.org, hirofumi@...l.parknet.co.jp,
	asit.k.mallick@...el.com
Subject: Re: REGRESSION: the new i386 timer code fails to sync CPUs

On 30 Jul 2006 22:10:05 +0200
Andi Kleen <ak@....de> wrote:

> > I guess Matthias didn't test this patch.  Can we get some obviously-correct
> > fix in place for 2.6.18?
> 
> So far we don't have any idea what the problem is on that system.

I believe we do know what the problem is: a) write_tsc() doesn't work, b)
the TSC's are unsynced (or have an offset), c) we removed a check which
would have caused pmtmr/rtc fallback.

> > It is a "CPU0: Intel(R) Xeon(TM) CPU 3.00GHz stepping 03".
> 
> Was that on that system?

yes.

> I guess it could be checked for and TSC 
> be forced off.

There's no need for that, I think.  synchronize_tsc_bp() knows for-sure
that the synchronization failed, in a way which works on all CPUs.

So all we need to do is to set some flag in synchronize_tsc_bp() if `buggy'
is set, telling the clocksource code to give up on the TSC.

> It sounds like a real CPU bug however.

I was hoping the Intel guys could help out with that.
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