Message-ID: <1438135759.2249.94.camel@stgolabs.net>
Subject: Re: Next round: revised futex(2) man page for review
From: Davidlohr Bueso <dave@stgolabs.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        "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>, 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>
Date: Tue, 28 Jul 2015 19:09:19 -0700
In-Reply-To: <20150728204508.GG19282@twins.programming.kicks-ass.net>
References: <55B61EF3.7080302@gmail.com>
	 <alpine.DEB.2.11.1507282054370.3825@nanos>
	 <20150728204508.GG19282@twins.programming.kicks-ass.net>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 983
Lines: 23

On Tue, 2015-07-28 at 22:45 +0200, Peter Zijlstra wrote:
> Also, this code seems to use plist, which means it won't do the right
> thing for SCHED_DEADLINE either.

Ick, I don't look forward to seeing nice futex plists converted into
rbtrees. As opposed to, eg. rtmutexes, there are a few caveats:

- Dealing with the top_waiter in rtmutexes is always easy, but in
futexes we need to deal with keys, so caching the leftmost won't work as
nicely.

- This will bloat things like futex_wake, where O(logN) is not suited
for FIFO iteration. And iterating linked lists is, in essence, all that
we really do when calling futex(2).

I have to wonder about the extra overhead added by these points.  I do
understand the dl concern, nonetheless.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/