linux-kernel - Re: Next round: revised futex(2) man page for review

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Date:	Tue, 28 Jul 2015 22:45:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Darren Hart <dvhart@...radead.org>,
	Torvald Riegel <triegel@...hat.com>,
	Carlos O'Donell <carlos@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, Jakub Jelinek <jakub@...hat.com>,
	linux-man <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Arnd Bergmann <arnd@...db.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux API <linux-api@...r.kernel.org>,
	Roland McGrath <roland@...k.frob.com>,
	Anton Blanchard <anton@...ba.org>,
	Eric Dumazet <edumazet@...gle.com>,
	bill o gallmeister <bgallmeister@...il.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Daniel Wagner <wagi@...om.org>, Rich Felker <dalias@...c.org>,
	Andy Lutomirski <luto@...capital.net>,
	bert hubert <bert.hubert@...herlabs.nl>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Heinrich Schuchardt <xypron.glpk@....de>
Subject: Re: Next round: revised futex(2) man page for review

On Tue, Jul 28, 2015 at 10:23:51PM +0200, Thomas Gleixner wrote:

> >        FUTEX_WAKE (since Linux 2.6.0)
> >               This  operation  wakes at most val of the waiters that are
> >               waiting (e.g., inside FUTEX_WAIT) on the futex word at the
> >               address  uaddr.  Most commonly, val is specified as either
> >               1 (wake up a single waiter) or INT_MAX (wake up all  wait‐
> >               ers).   No  guarantee  is provided about which waiters are
> >               awoken (e.g., a waiter with a higher  scheduling  priority
> >               is  not  guaranteed to be awoken in preference to a waiter
> >               with a lower priority).
> 
> That's only correct up to Linux 2.6.21.
> 
> Since 2.6.22 we have a priority ordered wakeup. For SCHED_OTHER
> threads this takes the nice level into account. Threads with the same
> priority are woken in FIFO order.

Maybe don't mention the effects of SCHED_OTHER, order by nice value is
'wrong'.

Also, this code seems to use plist, which means it won't do the right
thing for SCHED_DEADLINE either.

Do we want to go fix that?
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