linux-kernel - Re: [RFC][PATCH 1/8] rtmutex: Deboost before waking up the top waiter

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Date:	Tue, 14 Jun 2016 15:59:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Juri Lelli <juri.lelli@....com>
Cc:	mingo@...nel.org, tglx@...utronix.de, rostedt@...dmis.org,
	xlpang@...hat.com, linux-kernel@...r.kernel.org,
	mathieu.desnoyers@...icios.com, jdesfossez@...icios.com,
	bristot@...hat.com, Ingo Molnar <mingo@...hat.com>
Subject: Re: [RFC][PATCH 1/8] rtmutex: Deboost before waking up the top waiter

On Tue, Jun 14, 2016 at 02:20:31PM +0100, Juri Lelli wrote:
> On 14/06/16 14:54, Peter Zijlstra wrote:
> > On Tue, Jun 14, 2016 at 10:09:34AM +0100, Juri Lelli wrote:
> > > I've got only nitpicks for the changelog. Otherwise the patch looks good
> > > to me (and yes, without it bw inheritance would be a problem).
> > 
> > So for bw inheritance I'm still not sure how to dead with the faxt that
> > the top_pi_waiter, while blocked, can still be running, spin waiting.
> > 
> 
> You mean for M-BWI (multiprocessor), right? If that's the case, we were
> actually discussing this thing with Pisa/Trento folks yesterday. I'm not
> sure yet as well, but plan seems to be to get first things right with
> current DI code (Luca was saying that there is a BUG somewhere); then
> move to implement BWI; and then tackle the M- case (and see what we can
> do to work around the theoretical need for spin waiting). We actually
> got some ideas a while back, but I need to go there and refresh my mind.
> 
> If the plan sounds reasonable to you, it seems that we can start this
> discussion as soon as Luca has his DI fixes ready. What you think?

No objections.