From: Linus Torvalds <torvalds@linux-foundation.org>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: akpm@linux-foundation.org, Ingo Molnar <mingo@elte.hu>,
linux-kernel@vger.kernel.org,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Steven Rostedt <rostedt@goodmis.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Nicholas Miell <nmiell@comcast.net>,
laijs@cn.fujitsu.com, dipankar@in.ibm.com, josh@joshtriplett.org,
dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de,
peterz@infradead.org, Valdis.Kletnieks@vt.edu,
dhowells@redhat.com
Subject: Re: [patch 2/3] scheduler: add full memory barriers upon task switch at runqueue lock/unlock
Date: Mon, 1 Feb 2010 08:56:22 -0800 (PST) [thread overview]
Message-ID: <alpine.LFD.2.00.1002010854110.4206@localhost.localdomain> (raw)
In-Reply-To: <20100201164856.GA3486@Krystal>
On Mon, 1 Feb 2010, Mathieu Desnoyers wrote:
>
> What we have to be careful about here is that it's not enough to just
> rely on switch_mm() containing a memory barrier. What we really need to
> enforce is that switch_mm() issues memory barriers both _before_ and
> _after_ mm_cpumask modification. The "after" part is usually dealt with
> by the TLB context switch, but the "before" part usually isn't.
Ok, whatever. I vote for not doing anything at all, because this just all
sounds like some totally crazy crap. You haven't explained the actual
races, you haven't explained anything at all, you're apparently just
randomly sprinkling smp_mb's around until you think it's all fine.
Show the actual memory ordering constraints as it is related to the kernel
data structures. I'm totally uninterested in general handwaving and "we
must have smp_mb's here and here" without very explicit explanations of
exactly WHAT the memory orderings are.
Linus
next prev parent reply other threads:[~2010-02-01 16:58 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-31 20:52 [patch 0/3] introduce sys_membarrier(): process-wide memory barrier (v8) Mathieu Desnoyers
2010-01-31 20:52 ` [patch 1/3] Create spin lock/spin unlock with distinct memory barrier Mathieu Desnoyers
2010-02-01 7:25 ` Nick Piggin
2010-02-01 14:08 ` Mathieu Desnoyers
2010-02-01 7:28 ` Nick Piggin
2010-02-01 14:10 ` Mathieu Desnoyers
2010-02-01 15:22 ` Linus Torvalds
2010-02-01 15:41 ` Steven Rostedt
2010-01-31 20:52 ` [patch 2/3] scheduler: add full memory barriers upon task switch at runqueue lock/unlock Mathieu Desnoyers
2010-02-01 7:33 ` Nick Piggin
2010-02-01 9:42 ` Peter Zijlstra
2010-02-01 10:11 ` Nick Piggin
2010-02-01 10:36 ` Peter Zijlstra
2010-02-01 10:49 ` Nick Piggin
2010-02-01 14:47 ` Mathieu Desnoyers
2010-02-01 14:58 ` Nick Piggin
2010-02-01 15:23 ` Steven Rostedt
2010-02-01 15:44 ` Steven Rostedt
2010-02-01 16:00 ` Mike Galbraith
2010-02-01 15:27 ` Linus Torvalds
2010-02-01 16:09 ` Mathieu Desnoyers
2010-02-01 16:23 ` Linus Torvalds
2010-02-01 16:48 ` Mathieu Desnoyers
2010-02-01 16:56 ` Linus Torvalds [this message]
2010-02-01 17:45 ` Mathieu Desnoyers
2010-02-01 18:00 ` Steven Rostedt
2010-02-01 18:36 ` Linus Torvalds
2010-02-01 19:56 ` Mathieu Desnoyers
2010-02-01 20:42 ` Linus Torvalds
2010-02-01 22:42 ` Mathieu Desnoyers
2010-02-01 20:33 ` Steven Rostedt
2010-02-01 20:52 ` Linus Torvalds
2010-02-01 22:39 ` Steven Rostedt
2010-02-01 23:09 ` Steven Rostedt
2010-02-01 17:13 ` Steven Rostedt
2010-02-01 17:34 ` Linus Torvalds
2010-02-01 16:24 ` Steven Rostedt
2010-02-01 16:29 ` Peter Zijlstra
2010-02-01 16:46 ` Steven Rostedt
2010-02-01 16:11 ` Steven Rostedt
2010-01-31 20:52 ` [patch 3/3] introduce sys_membarrier(): process-wide memory barrier (v8) Mathieu Desnoyers
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