Re: Second soft lockup regression in yesterday's sched.git merge

[Peter Zijlstra <peterz@infradead.org>]

On Tue, 2008-04-22 at 23:39 -0700, David Miller wrote:
> Two changets after the buggy cpu_clock() changes, we have:
> 
> commit 15934a37324f32e0fda633dc7984a671ea81cd75
> Author: Guillaume Chazarain <guichaz@yahoo.fr>
> Date:   Sat Apr 19 19:44:57 2008 +0200
> 
>     sched: fix rq->clock overflows detection with CONFIG_NO_HZ
>     
>     When using CONFIG_NO_HZ, rq->tick_timestamp is not updated every TICK_NSEC.
>     We check that the number of skipped ticks matches the clock jump seen in
>     __update_rq_clock().
>     
>     Signed-off-by: Guillaume Chazarain <guichaz@yahoo.fr>
>     Signed-off-by: Ingo Molnar <mingo@elte.hu>
> 
> Which also causes softlockup warnings on my Niagara systems.
> 
> Note this is with the cpu_clock() change reverted, and the
> usual test case kernel build after a delay:
> 
> 	sleep 10m; time make -j64 >build.log 2>&1; make -j64 image

The effect of this one is that it should properly account idle time in
rq->clock when waking from nohz.

This 'extra' idle time would then propagate through cpu_clock() into the
softlockup code.

Could it be we touch the soft watchdog before we correct all these idle
times?