linux-kernel - RE: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single ipi fallback for smp_call_function

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Message-ID: <57C9024A16AD2D4C97DC78E552063EA36199197B@orsmsx505.amr.corp.intel.com>
Date:	Wed, 25 Feb 2009 10:25:04 -0800
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Nick Piggin <npiggin@...e.de>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Oleg Nesterov <oleg@...hat.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"steiner@....com" <steiner@....com>
Subject: RE: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single
 ipi fallback for smp_call_function_many())

> Just if I may add something -- I would probably slightly prefer if
> you explicitly used an sfence or other serializing instruction rather
> than smp_mb(). Maybe call it wrmsr_fence() or something. Apart from
> being self documenting, and less confusing (wrmsr is not part of
> normal ordering), I assume you technically also need it on UP
> systems?

Maybe I lost track of this thread ... but isn't this code for the
"send ipi" path?  On a UP system do we use IPI to interrupt ourself?
Even if we did, presumably we can't get inconsistencies if there is
only one cpu.

-Tony
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