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
Date: Thu, 16 Apr 2015 21:02:08 +0200 [thread overview]
Message-ID: <20150416190208.GD23123@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150416182426.GA17852@gmail.com>
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.
next prev parent reply other threads:[~2015-04-16 19:02 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-14 23:09 [PATCH 0/3] sched, timer: Improve scalability of itimers Jason Low
2015-04-14 23:09 ` [PATCH 1/3] sched, timer: Remove usages of ACCESS_ONCE in the scheduler Jason Low
2015-04-14 23:59 ` Steven Rostedt
2015-04-15 2:12 ` Jason Low
2015-04-15 2:40 ` Steven Rostedt
2015-04-15 7:46 ` Ingo Molnar
2015-04-15 18:49 ` Jason Low
2015-04-15 19:16 ` Steven Rostedt
2015-04-16 2:46 ` Jason Low
2015-04-16 16:52 ` Peter Zijlstra
2015-04-16 18:02 ` Ingo Molnar
2015-04-16 18:15 ` Peter Zijlstra
2015-04-16 18:24 ` Ingo Molnar
2015-04-16 19:02 ` Peter Zijlstra [this message]
2015-04-16 19:41 ` Paul E. McKenney
2015-04-17 3:25 ` Jason Low
2015-04-17 8:19 ` Ingo Molnar
2015-04-16 21:00 ` Jason Low
2015-04-16 2:29 ` Jason Low
2015-04-16 2:37 ` Steven Rostedt
2015-04-14 23:09 ` [PATCH 2/3] sched, timer: Use atomics for thread_group_cputimer to improve scalability Jason Low
2015-04-15 7:33 ` Ingo Molnar
2015-04-15 7:35 ` Ingo Molnar
2015-04-15 17:14 ` Jason Low
2015-04-15 10:37 ` Preeti U Murthy
2015-04-15 19:09 ` Jason Low
2015-04-15 13:25 ` Frederic Weisbecker
2015-04-15 13:32 ` Peter Zijlstra
2015-04-15 20:04 ` Jason Low
2015-04-15 14:23 ` Davidlohr Bueso
2015-04-15 21:15 ` Jason Low
2015-04-14 23:09 ` [PATCH 3/3] sched, timer: Use cmpxchg to do updates in update_gt_cputime() Jason Low
2015-04-14 23:53 ` [PATCH 0/3] sched, timer: Improve scalability of itimers Linus Torvalds
2015-04-15 7:24 ` Ingo Molnar
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