linux-kernel - Re: [PATCH] x86: Reenable TSC sync check at boot, even with NONSTOP

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Date:	Thu, 17 Dec 2009 13:00:23 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, H Peter Anvin <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Reenable TSC sync check at boot, even with
 NONSTOP_TSC

On Thu, 2009-12-17 at 13:27 -0700, Pallipadi, Venkatesh wrote:
> Commit 83ce4009 did the following change
> If the TSC is constant and non-stop, also set it reliable.
> 
> But, there seems to be few systems that will end up with TSC warp across
> sockets, depending on how the cpus come out of reset. Skipping TSC sync
> test on such systems may result in time inconsistency later.
> 
> So, reenable TSC sync test even on constant and non-stop TSC systems.
> Set, sched_clock_stable to 1 by default and reset it in
> mark_tsc_unstable, if TSC sync fails.
> 
> This change still gives perf benefit mentioned in 83ce4009 for systems
> where TSC is reliable.
> 
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>

Acked-by: Suresh Siddha <suresh.b.siddha@...el.com>

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