linux-kernel - Re: [patch] i386, numaq: enable TSCs again

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Message-ID: <20070525082537.GZ19966@holomorphy.com>
Date:	Fri, 25 May 2007 01:25:37 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Satyam Sharma <satyam.sharma@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [patch] i386, numaq: enable TSCs again

On Fri, May 25, 2007 at 01:19:44AM -0700, William Lee Irwin III wrote:
>> I remember. It was far beyond "slightly async;" they would drift
>> minutes apart during reasonable amounts of uptime, though it would take
>> at least several days to drift so far (I don't recall how long it took).

On Fri, May 25, 2007 at 10:22:59AM +0200, Andi Kleen wrote:
> sched_clock should handle that.

On Fri, May 25, 2007 at 01:19:44AM -0700, William Lee Irwin III wrote:
>> TSC synchronization is uniformly impossible on NUMA-Q. Bootlogs showing
>> the results of the attempts are still extant. They shouldn't end up too
>> far apart right after booting, but I don't have even ballpark estimates.
>> I'd hazard a guess of a few seconds.

On Fri, May 25, 2007 at 10:22:59AM +0200, Andi Kleen wrote:
> You should mark_tsc_instable(), but not tsc disable. In a release or two
> hopefully even that will be obsolete.

I don't have any particular preference here. I'm just donating a memory
dump. I have no intention of attempting to maintain NUMA-Q support code.


-- wli
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