linux-kernel - Re: futex: Allow FUTEX_CLOCK_REALTIME with FUTEX

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Message-ID: <alpine.DEB.2.11.1607062055570.4083@nanos>
Date:	Wed, 6 Jul 2016 20:57:59 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
cc:	Darren Hart <dvhart@...radead.org>,
	Matthieu CASTET <matthieu.castet@...rot.com>,
	linux-kernel@...r.kernel.org, Darren Hart <dvhart@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Eric Dumazet <dada1@...mosbay.com>
Subject: Re: futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op

On Thu, 23 Jun 2016, Michael Kerrisk (man-pages) wrote:
> On 06/23/2016 08:28 PM, Darren Hart wrote:
> > And as a follow-on, what is the reason for FUTEX_LOCK_PI only using
> > CLOCK_REALTIME? It seems reasonable to me that a user may want to wait a
> > specific amount of time, regardless of wall time.
> 
> Yes, that's another weird inconsistency.

The reason is that phtread_mutex_timedlock() uses absolute timeouts based on
CLOCK_REALTIME. glibc folks asked to make that the default behaviour back then
when we added LOCK_PI.

Thanks,

	tglx