linux-kernel - Re: [PATCH] configure HAVE_UNSTABLE_SCHED_CLOCK for SGI

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Date:	Tue, 6 Jan 2009 09:12:13 -0800
From:	Greg KH <greg@...ah.com>
To:	Dimitri Sivanich <sivanich@....com>
Cc:	linux-ia64@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Nick Piggin <npiggin@...e.de>, Tony Luck <tony.luck@...il.com>,
	Robin Holt <holt@....com>
Subject: Re: [PATCH] configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems

On Tue, Jan 06, 2009 at 10:27:41AM -0600, Dimitri Sivanich wrote:
> Turn on CONFIG_HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN.
> 
> SGI Altix has unsynchronized itc clocks.  This results in rq->clock
> occasionally being set to a time in the past by a remote cpu.
> 
> Note that it is possible that this problem may exist for other ia64
> machines as well, based on the following comment for sched_clock() in
> arch/ia64/kernel/head.S:
> 
>  * Return a CPU-local timestamp in nano-seconds.  This timestamp is
>  * NOT synchronized across CPUs its return value must never be
>  * compared against the values returned on another CPU.  The usage in
>  * kernel/sched.c ensures that.
> 
> 
> Signed-off-by: Dimitri Sivanich <sivanich@....com>
> 
> ---
> 
> Greg, if everyone is OK with this patch, this should also be applied
> to all stable trees starting with 2.6.26.

That's fine (but 2.6.26 is no longer getting -stable releases).

Just let stable@...nel.org know when this patch is applied in Linus's
tree.  You can do this automatically by adding a:
	Cc: stable <stable@...nel.org>
to the signed-off-by: area of the patch, and the stable team will be
automatically notified when it goes into Linus's tree.

thanks,

greg k-h
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