Messages in this thread Patch in this message | | | Subject | Re: [PATCH] sched_clock: prevent scd->clock from moving backwards | From | Dave Kleikamp <> | Date | Thu, 09 Oct 2008 12:54:22 -0500 |
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On Thu, 2008-10-09 at 17:17 +0200, Ingo Molnar wrote:
> hm, -tip testing found a sporadic hard lockup during bootup, and i've > bisected it back to this patch. They happened on 64-bit test-systems. > I've attached the .config that produced the problem. > > i reverted the patch and the lockups went away. But i cannot see what's > wrong with it ...
I could have sworn I ran with the patch, but maybe I got my patch queue messed up and never tested it right.
I think I see the problem.
--- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -118,13 +118,13 @@ static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now) /* * scd->clock = clamp(scd->tick_gtod + delta, - * max(scd->tick_gtod, scd->clock), - * scd->tick_gtod + TICK_NSEC); + * max(scd->tick_gtod, scd->clock), + * min(scd->clock, scd->tick_gtod + TICK_NSEC)); */ clock = scd->tick_gtod + delta; min_clock = wrap_max(scd->tick_gtod, scd->clock); - max_clock = scd->tick_gtod + TICK_NSEC; + max_clock = wrap_min(scd->clock, scd->tick_gtod + TICK_NSEC); clock = wrap_max(clock, min_clock); clock = wrap_min(clock, max_clock); We want wrap_max(scd->clock, scd->tick_gtod + TICK_NSEC), not wrap_min(). The problem I am trying to fix is that scd->tick_gtod + TICK_NSEC may be too low. The upper bound needs to be at LEAST scd->clock. Limiting it to scd->clock all the time is disastrous. :-)
I'll fix the patch and retest it before sending it again.
Sorry about my sloppiness.
Shaggy -- David Kleikamp IBM Linux Technology Center
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