Re: [PATCH] rcu: Eliminate softirq processing from rcutree

[Mike Galbraith]

On Sat, 2014-01-25 at 06:12 +0100, Mike Galbraith wrote: 
> On Fri, 2014-01-24 at 20:50 +0100, Sebastian Andrzej Siewior wrote: 
> > * Mike Galbraith | 2014-01-18 04:25:14 [+0100]:
> > 
> > >> ># timers-do-not-raise-softirq-unconditionally.patch
> > >> ># rtmutex-use-a-trylock-for-waiter-lock-in-trylock.patch
> > >> >
> > >> >..those two out does seem to have stabilized the thing.
> > >> 
> > >> timers-do-not-raise-softirq-unconditionally.patch is on its way out.
> > >> 
> > >> rtmutex-use-a-trylock-for-waiter-lock-in-trylock.patch confues me.
> > >> Didn't you report once that your box deadlocks without this patch? Now
> > >> your 64way box on the other hand does not work with it?
> > >
> > >If 'do not raise' is applied, 'use a trylock' won't save you.  If 'do
> > is this just an observation or you do know why it won't save me?
> 
> It's an observation from beyond the grave from the 64 core box that it
> repeatedly did NOT save :)  Autopsy photos below.
> 
> I've built 3.12.8-rt9 with Stevens v2 "timer: Raise softirq if there's
> irq_work" to see if it'll survive.

And it did, configured both as nohz_tick, and nohz_full_all.  The irqs
are enabled warning in can_stop_full_tick() fired for nohz_full_all, but
that's it.

For grins, I also applied Paul's v3 timer latency series while testing
nohz_full_all config.   The box was heavily loaded the vast majority of
the time, but it didn't explode or do anything obviously evil.

-Mike

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