linux-kernel - Re: [PATCH] locking/rwsem: Make owner store task pointer of last owning reader

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Message-ID: <20180911193824.GW24106@hirez.programming.kicks-ass.net>
Date:   Tue, 11 Sep 2018 21:38:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] locking/rwsem: Make owner store task pointer of last
 owning reader

On Tue, Sep 11, 2018 at 12:21:22PM -0700, Davidlohr Bueso wrote:
> On Mon, 10 Sep 2018, Peter Zijlstra wrote:
> 
> > [ RT has something along those lines, and I have half a patch that
> >  starts doing that too, but I never found enough time to really work on
> >  it :-( ]
> 
> But don't rt rwsems act pretty much like a regular mutex in that it only
> allows readers to nest, not share the lock because of priority inversion
> scenarios.
> 
> Also, wrt rtmutex, will that top-spinner thing ever make it in?

Nah, tglx rewrote that a while ago. It's something semi clever now.
Lemme see if I can find the patch.

  https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/kernel/locking/rwsem-rt.c?h=linux-4.18.y-rt&id=1a42d0b3c3f34895cb5d63e1cd2be02f6077919b