Re: [PATCH] sched_clock: prevent scd->clock from moving backwards

[Ingo Molnar]

* Dave Kleikamp <shaggy@xxxxxxxxxxxxxxxxxx> wrote:

> On Thu, 2008-10-09 at 12:54 -0500, Dave Kleikamp wrote:
> 
> > I'll fix the patch and retest it before sending it again.
> 
> I'm definitely running with the new patch now.  Here goes:
>  -------------------------------------------------
> sched_clock: prevent scd->clock from moving backwards
> 
> When sched_clock_cpu() couples the clocks between two cpus, it may
> increment scd->clock beyond the GTOD tick window that __update_sched_clock()
> uses to clamp the clock.  A later call to __update_sched_clock() may move
> the clock back to scd->tick_gtod + TICK_NSEC, violating the clock's
> monotonic property.
> 
> This patch ensures that scd->clock will not be set backward.
> 
> Signed-off-by: Dave Kleikamp <shaggy@xxxxxxxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>

applied to tip/sched/clock, thanks Dave!

	Ingo
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