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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Roman Pen <roman.penyaev@profitbricks.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	andrea.parri@amarulasolutions.com,
	Will Deacon <will.deacon@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Boqun Feng <boqun.feng@gmail.com>,
	Nick Piggin <npiggin@gmail.com>,
	David Howells <dhowells@redhat.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	Akira Yokosawa <akiyks@gmail.com>, Ingo Molnar <mingo@kernel.org>
Subject: Re: LKMM litmus test for Roman Penyaev's rcu-rr
Date: Thu, 7 Jun 2018 08:06:51 -0700	[thread overview]
Message-ID: <CA+55aFzs0ueN22WaKs_R6=T4HHY9j0MtpoFA8eh=t=PN7grCnA@mail.gmail.com> (raw)
In-Reply-To: <20180607094314.GF3593@linux.vnet.ibm.com>

On Thu, Jun 7, 2018 at 2:41 AM Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
>
> We are considering adding unmarked accesses, for example, accesses
> protected by locks.  One possible litmus test (not yet supported!)
> might look like this:

Fair enough - you do want to have the distinction between "marked" and
"unmarked".

And it does make sense, although at that point I think you do hit the
"what can a compiler do" issue more. Right now, I think the things you
check are all pretty much "compiler can't do a lot of movement".

But I suspect that the markings you do have are going to be fairly
limited. Things like "READ_ONCE()" vs "smp_read_acquire()" are still
fairly simple from a compiler standpoint, at least when it comes to
control flow - they have "side effects". So I guess that's the only
real difference there - a regular read doesn't have side effects, so
it could be moved up past a conditional, and/or duplicated for each
use. That sounds much more complex to the checker than the existing
things it supports, no?

               Linus

  parent reply	other threads:[~2018-06-07 15:07 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-28 22:08 LKMM litmus test for Roman Penyaev's rcu-rr Paul E. McKenney
2018-05-29 18:35 ` Alan Stern
2018-05-29 19:03   ` Paul E. McKenney
2018-05-29 20:49     ` Alan Stern
2018-05-29 21:10       ` Linus Torvalds
2018-05-29 22:53         ` Paul E. McKenney
2018-05-30 14:46           ` Alan Stern
2018-05-30 14:29         ` Alan Stern
2018-05-30 14:59           ` Linus Torvalds
2018-05-30 18:10             ` Alan Stern
2018-05-30 18:38             ` Paul E. McKenney
2018-05-30 19:08               ` Alan Stern
2018-05-30 19:45                 ` Paul E. McKenney
2018-05-30 20:28                   ` Alan Stern
2018-05-30 21:49                     ` Paul E. McKenney
2018-05-30 22:01                 ` Linus Torvalds
2018-05-30 23:14                   ` Paul E. McKenney
2018-05-31 14:27                     ` Alan Stern
2018-06-02 14:44                       ` Paul E. McKenney
2018-06-04 14:17                         ` Alan Stern
2018-06-04 16:01                           ` Paul E. McKenney
2018-06-06  9:40                 ` Roman Penyaev
2018-06-06 13:54                   ` Alan Stern
2018-06-06 14:41                     ` Roman Penyaev
2018-06-06 15:55                       ` Alan Stern
2018-06-06 19:07                   ` Paul E. McKenney
2018-06-06 19:23                     ` Linus Torvalds
2018-06-07  9:43                       ` Paul E. McKenney
2018-06-07 14:57                         ` Alan Stern
2018-06-07 15:40                           ` Linus Torvalds
2018-06-07 15:06                         ` Linus Torvalds [this message]
2018-06-07 19:57                           ` Paul E. McKenney

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