linux-kernel - Re: [PATCH RT] kernel/futex: don't deboost too early

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Message-ID: <alpine.DEB.2.20.1609302041410.5508@nanos>
Date:   Fri, 30 Sep 2016 20:43:26 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        peterz@...radead.org
Subject: Re: [PATCH RT] kernel/futex: don't deboost too early

On Fri, 30 Sep 2016, Steven Rostedt wrote:
> This looks awfully complex. Would something as simple as this work?
> 
> What harm can happen by moving the holding of the lock after the
> wakeups for RT?

That's exactly bringing us back to the state before we added the delayed
wakeup so that the woken waiter will not be blocked on hb->lock right
away. That's 2 extra context switches for nothing.

Thanks,

	tglx