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

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Message-ID: <20160930161045.hueqm3pesy3yqkps@linutronix.de>
Date:   Fri, 30 Sep 2016 18:10:45 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, peterz@...radead.org
Subject: Re: [PATCH RT] kernel/futex: don't deboost too early

On 2016-09-30 12:00:38 [-0400], 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?
If the waiter has a higher priority he will get on the CPU and remove
_this_ task. Since the woken up task will access the hb lock
immediately _or_ before going to sleep so it will boost in order to get
the hb lock.
That is way we introduced this delayed wake up in the first place.

Sebastian