Re: [PATCH] configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems

Greg KH
2009-01-06T17:12:13Z

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@sgi.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@kernel.org know when this patch is applied in Linus's
tree. You can do this automatically by adding a:
Cc: stable <stable@kernel.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