From: Suresh Siddha <suresh.b.siddha@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>,
"Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>,
Yinghai Lu <yinghai@kernel.org>, Nick Piggin <npiggin@suse.de>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Oleg Nesterov <oleg@redhat.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Jens Axboe <jens.axboe@oracle.com>,
Rusty Russell <rusty@rustcorp.com.au>,
Steven Rostedt <rostedt@goodmis.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
asit.k.mallick@intel.com
Subject: Re: Q: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single ipi fallback for smp_call_function_many())
Date: Wed, 18 Feb 2009 10:33:46 -0800 [thread overview]
Message-ID: <1234982026.29823.17.camel@vayu> (raw)
In-Reply-To: <alpine.LFD.2.00.0902180913110.21686@localhost.localdomain>
On Wed, 2009-02-18 at 09:14 -0800, Linus Torvalds wrote:
>
> On Wed, 18 Feb 2009, Ingo Molnar wrote:
> >
> > an off-list comment pointed out this piece of information as
> > well:
> >
> > http://www.sandpile.org/ia32/coherent.htm
> >
> > A WRMSR to one of the x2APIC MSRs (0000_0800h...0000_0BFFh) is
> > not guaranteed to be serializing.
> >
> > So i suspect we should just enclose it in smp_mb() pairs to make
> > sure it's a full barrier in both directions?
>
> Why would we care about "both directions"?
on x86 we don't need in both directions.
>
> I think putting an sfence _before_ the wrmsr (and not even all of them -
> just put it in front of the "send IPI" sequence) should be fine. Any other
> ordering sounds like just unnecessary overhead to me.
For x2apic ipi's, we should use a serializing instruction or a "mfence"
instruction. "sfence" will not help in this scenario.
thanks,
suresh
next prev parent reply other threads:[~2009-02-18 18:35 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
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[not found] ` <20090217101130.GA8660@wotan.suse.de>
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2009-02-17 11:26 ` Q: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single ipi fallback for smp_call_function_many()) Nick Piggin
2009-02-17 11:48 ` Peter Zijlstra
2009-02-17 15:51 ` Paul E. McKenney
2009-02-18 2:15 ` Suresh Siddha
2009-02-18 2:40 ` Paul E. McKenney
2009-02-17 19:28 ` Q: " Oleg Nesterov
2009-02-17 21:32 ` Paul E. McKenney
2009-02-17 21:45 ` Oleg Nesterov
2009-02-17 22:39 ` Paul E. McKenney
2009-02-18 13:52 ` Nick Piggin
2009-02-18 16:09 ` Linus Torvalds
2009-02-18 16:21 ` Ingo Molnar
2009-02-18 16:21 ` Ingo Molnar
2009-02-18 16:33 ` Linus Torvalds
2009-02-18 16:58 ` Ingo Molnar
2009-02-18 17:05 ` Ingo Molnar
2009-02-18 17:10 ` Ingo Molnar
2009-02-18 17:17 ` Linus Torvalds
2009-02-18 17:23 ` Ingo Molnar
2009-02-18 17:14 ` Linus Torvalds
2009-02-18 17:47 ` Ingo Molnar
2009-02-18 18:33 ` Suresh Siddha [this message]
2009-02-18 16:37 ` Gleb Natapov
2009-02-19 0:12 ` Nick Piggin
2009-02-19 6:47 ` Benjamin Herrenschmidt
2009-02-19 13:11 ` Nick Piggin
2009-02-19 13:11 ` Nick Piggin
2009-02-19 15:06 ` Ingo Molnar
2009-02-19 21:49 ` Benjamin Herrenschmidt
2009-02-18 2:21 ` Suresh Siddha
2009-02-18 13:59 ` Nick Piggin
2009-02-18 16:19 ` Linus Torvalds
2009-02-18 16:23 ` Ingo Molnar
2009-02-18 18:43 ` Suresh Siddha
2009-02-18 19:17 ` Ingo Molnar
2009-02-18 23:55 ` Suresh Siddha
2009-02-19 12:20 ` Ingo Molnar
2009-02-19 12:29 ` Nick Piggin
2009-02-19 12:45 ` Ingo Molnar
2009-02-19 22:00 ` Suresh Siddha
2009-02-20 10:56 ` Ingo Molnar
2009-02-20 18:56 ` Suresh Siddha
2009-02-20 18:56 ` Suresh Siddha
2009-02-20 19:40 ` Ingo Molnar
2009-02-20 23:28 ` Jack Steiner
2009-02-25 3:32 ` Nick Piggin
2009-02-25 12:47 ` Ingo Molnar
2009-02-25 18:25 ` Luck, Tony
2009-03-17 18:16 ` Suresh Siddha
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