Date: Tue, 28 Jul 2015 23:03:52 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        Darren Hart <dvhart@infradead.org>,
        Torvald Riegel <triegel@redhat.com>,
        "Carlos O'Donell" <carlos@redhat.com>, Ingo Molnar <mingo@elte.hu>,
        Jakub Jelinek <jakub@redhat.com>,
        linux-man <linux-man@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Davidlohr Bueso <dave@stgolabs.net>, Arnd Bergmann <arnd@arndb.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linux API <linux-api@vger.kernel.org>,
        Roland McGrath <roland@hack.frob.com>,
        Anton Blanchard <anton@samba.org>, Eric Dumazet <edumazet@google.com>,
        bill o gallmeister <bgallmeister@gmail.com>,
        Jan Kiszka <jan.kiszka@siemens.com>, Daniel Wagner <wagi@monom.org>,
        Rich Felker <dalias@libc.org>, Andy Lutomirski <luto@amacapital.net>,
        bert hubert <bert.hubert@netherlabs.nl>,
        Rusty Russell <rusty@rustcorp.com.au>,
        Heinrich Schuchardt <xypron.glpk@gmx.de>
Subject: Re: Next round: revised futex(2) man page for review
In-Reply-To: <20150728204508.GG19282@twins.programming.kicks-ass.net>
Message-ID: <alpine.DEB.2.11.1507282303290.3825@nanos>
References: <55B61EF3.7080302@gmail.com> <alpine.DEB.2.11.1507282054370.3825@nanos> <20150728204508.GG19282@twins.programming.kicks-ass.net>
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On Tue, 28 Jul 2015, Peter Zijlstra wrote:

> 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'.

Indeed.
 
> 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?

I think so.

Thanks,

	tglx

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