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

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Message-ID: <20160614132031.GL5981@e106622-lin>
Date:	Tue, 14 Jun 2016 14:20:31 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Peter Zijlstra <peterz@...radead.org>
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 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?