linux-kernel - Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule

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Date:	Thu, 07 Apr 2016 21:04:40 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule

On Thu, 2016-04-07 at 18:47 +0200, Sebastian Andrzej Siewior wrote:
> On 04/02/2016 05:12 AM, Mike Galbraith wrote:
> > > By the time I improved hotplug I played with this. I had a few ideas but
> > > it didn't fly in the end. Today however I ended up with this:
> > 
> > Yeah, but that fails the duct tape test too.  Mine is below, and is the
> > extra sticky variety ;-)  With busted 0299 patch reverted and those two
> > applied, my DL980 took a beating for ~36 hours before I aborted it.. ie
> > hotplug road seemingly has no more -rt specific potholes.
> 
> just to be clear: The patch I attached did _not_ work for you.

Sorry, I didn't test.  Marathon stress test session convinced me that
the lock added by -rt absolutely had to die.

> > If that lock dies, we can unpin when entering lock slow path and pin
> > again post acquisition with no ABBA worries as well, and not only does
> > existing hotplug work heaping truckloads better, -rt can perhaps help
> > spot trouble as the rewrite proceeds.
> > 
> > Current state is more broken than ever.. if that's possible.
> 
> And the two patches you attached here did?

I've killed way too many NOPREEMPT kernels to make any rash -rt claims.
 What I can tell you is that my 64 core DL980 running 4.6-rc2-rt13 plus
the two posted patches survived for ~20 hours before I had to break it
off because I needed the box. 

These two haven't been through _as_ much pounding as the two targeted
bandaids I showed have, but have been through quite a bit.  Other folks
beating the living crap outta their boxen too would not be a bad idea.

	-Mike