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From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Daniel Colascione <dancol@google.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	boqun.feng@gmail.com, luto@amacapital.net, davejwatson@fb.com,
	linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
	Paul Turner <pjt@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux@arm.linux.org.uk, mingo@redhat.com, hpa@zytor.com,
	Andrew Hunter <ahh@google.com>,
	andi@firstfloor.org, cl@linux.com, bmaurer@fb.com,
	rostedt@goodmis.org, josh@joshtriplett.org,
	torvalds@linux-foundation.org, catalin.marinas@arm.com,
	will.deacon@arm.com,
	Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
	Joel Fernandes <joelaf@google.com>
Subject: Re: [RFC PATCH for 4.18 00/14] Restartable Sequences
Date: Sun, 6 May 2018 12:03:32 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1805061202550.1685@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20180502202233.GV12217@hirez.programming.kicks-ass.net>

On Wed, 2 May 2018, Peter Zijlstra wrote:

> On Wed, May 02, 2018 at 06:27:22PM +0000, Daniel Colascione wrote:
> > On Wed, May 2, 2018 at 10:22 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >> On Wed, May 02, 2018 at 03:53:47AM +0000, Daniel Colascione wrote:
> > > > Suppose we make a userspace mutex implemented with a lock word having
> > three
> > > > bits: acquired, sleep_mode, and wait_pending, with the rest of the word
> > not
> > > > being relevant at the moment.
> > 
> > > So ideally we'd kill FUTEX_WAIT/FUTEX_WAKE for mutexes entirely, and go
> > > with FUTEX_LOCK/FUTEX_UNLOCK that have the same semantics as the
> > > existing FUTEX_LOCK_PI/FUTEX_UNLOCK_PI, namely, the word contains the
> > > owner TID.
> > 
> > That doesn't work if you want to use the rest of the word for something
> > else, like a recursion count. With FUTEX_WAIT and FUTEX_WAKE, you can make
> > a lock with two bits.
> 
> Recursive locks are teh most horrible crap ever. And having the tid in
> the word allows things like kernel based optimistic spins and possibly
> PI related things.

FWIW, robust futex have also the TID requirement.

Thanks,

	tglx

      parent reply	other threads:[~2018-05-06 10:03 UTC|newest]

Thread overview: 105+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-30 22:44 [RFC PATCH for 4.18 00/14] Restartable Sequences Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 01/14] uapi headers: Provide types_32_64.h (v2) Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 02/14] rseq: Introduce restartable sequences system call (v13) Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-05-16 16:24   ` Peter Zijlstra
2018-05-16 16:24     ` Peter Zijlstra
2018-05-16 20:18     ` Mathieu Desnoyers
2018-05-16 20:18       ` Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 03/14] arm: Add restartable sequences support Mathieu Desnoyers
2018-05-16 16:18   ` Peter Zijlstra
2018-05-16 16:18     ` Peter Zijlstra
2018-05-16 20:13     ` Mathieu Desnoyers
2018-05-16 20:13       ` Mathieu Desnoyers
2018-05-17 13:32       ` Will Deacon
2018-05-17 13:32         ` Will Deacon
2018-05-17 15:30         ` Mathieu Desnoyers
2018-05-17 15:30           ` Mathieu Desnoyers
2018-05-22 18:19           ` Mathieu Desnoyers
2018-05-22 18:19             ` Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 04/14] arm: Wire up restartable sequences system call Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 05/14] x86: Add support for restartable sequences (v2) Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 06/14] x86: Wire up restartable sequence system call Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 07/14] powerpc: Add support for restartable sequences Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-05-16 16:18   ` Peter Zijlstra
2018-05-16 16:18     ` Peter Zijlstra
2018-05-16 20:13     ` Mathieu Desnoyers
2018-05-16 20:13       ` Mathieu Desnoyers
2018-05-17  1:19       ` Boqun Feng
2018-05-17  1:19         ` Boqun Feng
2018-05-17  1:19         ` Boqun Feng
2018-05-17  7:43         ` Peter Zijlstra
2018-05-17  7:43           ` Peter Zijlstra
2018-05-17 15:28         ` Mathieu Desnoyers
2018-05-17 15:28           ` Mathieu Desnoyers
2018-05-17 23:50           ` Boqun Feng
2018-05-17 23:50             ` Boqun Feng
2018-05-18 18:17             ` Mathieu Desnoyers
2018-05-18 18:17               ` Mathieu Desnoyers
2018-05-20 14:08               ` Boqun Feng
2018-05-20 14:08                 ` Boqun Feng
2018-05-20 14:08                 ` Boqun Feng
2018-05-23 20:14                 ` Mathieu Desnoyers
2018-05-23 20:14                   ` Mathieu Desnoyers
2018-05-23 20:46                   ` Paul E. McKenney
2018-05-23 20:46                     ` Paul E. McKenney
2018-05-23 21:29                   ` Mathieu Desnoyers
2018-05-23 21:29                     ` Mathieu Desnoyers
2018-05-24  1:03                     ` Michael Ellerman
2018-05-24  1:03                       ` Michael Ellerman
2018-05-28  7:00                       ` Mathieu Desnoyers
2018-05-28  7:00                         ` Mathieu Desnoyers
2018-05-18 12:38           ` Michael Ellerman
2018-05-18 12:38             ` Michael Ellerman
2018-04-30 22:44 ` [PATCH 08/14] powerpc: Wire up restartable sequences system call Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 09/14] selftests: lib.mk: Introduce OVERRIDE_TARGETS Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` mathieu.desnoyers
2018-04-30 22:44 ` [PATCH 10/14] rseq: selftests: Provide rseq library (v5) Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` mathieu.desnoyers
2018-04-30 22:44 ` [PATCH 11/14] rseq: selftests: Provide basic test Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` mathieu.desnoyers
2018-04-30 22:44 ` [PATCH 12/14] rseq: selftests: Provide basic percpu ops test (v2) Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` mathieu.desnoyers
2018-04-30 22:44 ` [PATCH 13/14] rseq: selftests: Provide parametrized tests (v2) Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` mathieu.desnoyers
2018-04-30 22:44 ` [PATCH 14/14] rseq: selftests: Provide Makefile, scripts, gitignore (v2) Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` Mathieu Desnoyers
2018-04-30 22:44   ` mathieu.desnoyers
2018-05-02  3:53 ` [RFC PATCH for 4.18 00/14] Restartable Sequences Daniel Colascione
2018-05-02  8:43   ` Peter Zijlstra
2018-05-02 16:03   ` Mathieu Desnoyers
2018-05-02 16:03     ` Mathieu Desnoyers
2018-05-02 16:07     ` Daniel Colascione
2018-05-02 16:42       ` Steven Rostedt
2018-05-02 16:55         ` Daniel Colascione
2018-05-03 16:12       ` Mathieu Desnoyers
2018-05-03 16:12         ` Mathieu Desnoyers
2018-05-03 16:22         ` Daniel Colascione
2018-05-03 18:04           ` Mathieu Desnoyers
2018-05-03 18:04             ` Mathieu Desnoyers
2018-05-03 16:48         ` Joel Fernandes
2018-05-03 17:18           ` Daniel Colascione
2018-05-03 17:46             ` Joel Fernandes
2018-05-03 17:46               ` Joel Fernandes
2018-05-04 22:17               ` Ben Maurer
2018-05-04 22:17                 ` Ben Maurer
2018-05-02 17:22   ` Peter Zijlstra
2018-05-02 18:27     ` Daniel Colascione
2018-05-02 20:22       ` Peter Zijlstra
2018-05-02 20:37         ` Daniel Colascione
2018-05-03  1:15           ` Steven Rostedt
2018-05-03  8:49           ` Peter Zijlstra
2018-05-06 10:03         ` Thomas Gleixner [this message]

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