Message-ID: <1390842228.5425.175.camel@marge.simpson.net>
Subject: Re: [PATCH] rcu: Eliminate softirq processing from rcutree
From: Mike Galbraith <bitbucket@online.de>
To: paulmck@linux.vnet.ibm.com
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        linux-rt-users@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 27 Jan 2014 18:03:48 +0100
In-Reply-To: <20140127165405.GK9012@linux.vnet.ibm.com>
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	 <1390015514.5444.46.camel@marge.simpson.net>
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On Mon, 2014-01-27 at 08:54 -0800, Paul E. McKenney wrote: 
> On Mon, Jan 27, 2014 at 06:10:44AM +0100, Mike Galbraith wrote:
> > 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.
> 
> Cool!  May I add your Tested-by?

Certainly.

-Mike

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