Date: Thu, 16 Apr 2015 21:02:08 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, Mel Gorman <mel@csn.ul.ie>,
        Rik van Riel <riel@redhat.com>, Jason Low <jason.low2@hp.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, Mel Gorman <mgorman@suse.de>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>, hideaki.kimura@hp.com,
        Aswin Chandramouleeswaran <aswin@hp.com>,
        Scott J Norton <scott.norton@hp.com>
Subject: Re: [PATCH 1/3] sched, timer: Remove usages of ACCESS_ONCE in the
 scheduler
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On Thu, Apr 16, 2015 at 08:24:27PM +0200, Ingo Molnar wrote:
> Yes ... but that still leaves this weird feeling that it's really 
> still a bit wrong because it's not proper parallel code, we just 
> reduced the probability of the remaining races radically. And it's not 
> like GCC (or any compiler) does load tearing or even store tearing 
> under normal -O2 for such code patterns, right?

I think Paul once caught GCC doing something silly, but typically no.
The re-loads however have been frequently observed.

> > And its not like they really cost anything.
> 
> That's true.
> 
> Would it make sense to add a few comments to the seq field definition 
> site(s), about how it's supposed to be accessed - or to the 
> READ_ONCE()/WRITE_ONCE() sites, to keep people from wondering?

For sure, can do a comment no problem.
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