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From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alan Stern <stern@rowland.harvard.edu>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	rostedt <rostedt@goodmis.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Boqun Feng <boqun.feng@gmail.com>,
	Will Deacon <will.deacon@arm.com>,
	David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates
Date: Tue, 20 Aug 2019 13:31:35 -0700	[thread overview]
Message-ID: <20190820203135.GX28441@linux.ibm.com> (raw)
In-Reply-To: <20190820140116.GT2332@hirez.programming.kicks-ass.net>

On Tue, Aug 20, 2019 at 04:01:16PM +0200, Peter Zijlstra wrote:
> On Fri, Aug 16, 2019 at 09:52:17PM -0700, Paul E. McKenney wrote:
> > On Fri, Aug 16, 2019 at 03:57:43PM -0700, Linus Torvalds wrote:
> > 
> > [ . . . ]
> > 
> > > We add READ_ONCE and WRITE_ONCE annotations when they make sense. Not
> > > because of some theoretical "compiler is free to do garbage"
> > > arguments. If such garbage happens, we need to fix the compiler, the
> > > same way we already do with
> > > 
> > >   -fno-strict-aliasing
> > 
> > Yeah, the compete-with-FORTRAN stuff.  :-/
> > 
> > There is some work going on in the C committee on this, where the
> > theorists would like to restrict strict-alias based optimizations to
> > enable better analysis tooling.  And no, although the theorists are
> > pushing in the direction we would like them to, as far as I can see
> > they are not pushing as far as we would like.  But it might be that
> > -fno-strict-aliasing needs some upgrades as well.  I expect to learn
> > more at the next meeting in a few months.
> > 
> > http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2364.pdf
> > http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2363.pdf
> > http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2362.pdf
> 
> We really should get the compiler folks to give us a
> -fno-pointer-provenance. Waiting on the standards committee to get their
> act together seems unlikely, esp. given that some people actually seem
> to _want_ this nonsense :/

The reason that they want it is to enable some significant optimizations
in numerical code on the one hand and in heavily templated C++ code on
the other.  Neither of which has much bearing on kernel code.

Interested in coming to the next C standards committee meeting in October
to help me push for this?  ;-)

							Thanx, Paul

  reply	other threads:[~2019-08-20 20:32 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-18 10:29 WARNING in tracepoint_probe_register_prio (3) syzbot
2019-08-16  0:11 ` syzbot
2019-08-16 14:26   ` [PATCH 1/1] Fix: trace sched switch start/stop racy updates Mathieu Desnoyers
2019-08-16 16:25     ` Steven Rostedt
2019-08-16 16:48       ` Valentin Schneider
2019-08-16 17:04         ` Steven Rostedt
2019-08-16 17:41           ` Mathieu Desnoyers
2019-08-16 19:18             ` Steven Rostedt
2019-08-16 19:19             ` Alan Stern
2019-08-16 20:44               ` Joel Fernandes
2019-08-16 20:49                 ` Thomas Gleixner
2019-08-16 20:57                   ` Joel Fernandes
2019-08-16 22:27                     ` Valentin Schneider
2019-08-16 22:57                       ` Linus Torvalds
2019-08-17  1:41                         ` Mathieu Desnoyers
2019-08-17  4:52                         ` Paul E. McKenney
2019-08-17  8:28                           ` Linus Torvalds
2019-08-17  8:44                             ` Linus Torvalds
2019-08-17 15:02                               ` Mathieu Desnoyers
2019-08-17 20:03                                 ` Valentin Schneider
2019-08-17 23:00                                   ` Paul E. McKenney
2019-08-19 10:34                                     ` Valentin Schneider
2019-08-17 22:28                             ` Paul E. McKenney
2019-08-20 14:01                           ` Peter Zijlstra
2019-08-20 20:31                             ` Paul E. McKenney [this message]
2019-08-20 20:39                               ` Peter Zijlstra
2019-08-20 20:52                                 ` Paul E. McKenney
2019-08-16 21:04                   ` Linus Torvalds
2019-08-17  1:36                     ` Mathieu Desnoyers
2019-08-17  2:13                       ` Steven Rostedt
2019-08-17 14:40                         ` Mathieu Desnoyers
2019-08-17 15:26                           ` Steven Rostedt
2019-08-17 15:55                             ` Mathieu Desnoyers
2019-08-17 16:40                               ` Steven Rostedt
2019-08-17 22:06                                 ` Paul E. McKenney
2019-08-17  8:08                       ` Linus Torvalds
2019-08-20 13:56                         ` Peter Zijlstra
2019-08-20 20:29                           ` Paul E. McKenney
2019-08-21 10:32                             ` Will Deacon
2019-08-21 13:23                               ` Paul E. McKenney
2019-08-21 13:32                                 ` Will Deacon
2019-08-21 13:56                                   ` Paul E. McKenney
2019-08-21 16:22                                     ` Will Deacon
2019-08-21 15:33                                 ` Peter Zijlstra
2019-08-21 15:48                                   ` Mathieu Desnoyers
2019-08-21 16:14                                     ` Paul E. McKenney
2019-08-21 19:03                                     ` Joel Fernandes
2019-09-09  6:21                           ` Herbert Xu
2019-08-16 20:49                 ` Steven Rostedt
2019-08-16 20:59                   ` Joel Fernandes
2019-08-17  1:25                   ` Mathieu Desnoyers
2019-08-18  9:15                   ` stable markup was " Pavel Machek
2019-08-16 17:19       ` Mathieu Desnoyers
2019-08-16 19:15         ` Steven Rostedt
2019-08-17 14:27           ` Mathieu Desnoyers
2019-08-17 15:42             ` Steven Rostedt
2019-08-17 15:53               ` Mathieu Desnoyers
2019-08-17 16:43                 ` Steven Rostedt
2019-08-16 12:32 ` WARNING in tracepoint_probe_register_prio (3) syzbot
2019-08-16 12:41   ` Sebastian Andrzej Siewior

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