linux-kernel - Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier (v5)

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Message-ID: <20100113155845.GA6803@linux.vnet.ibm.com>
Date:	Wed, 13 Jan 2010 07:58:45 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Nicholas Miell <nmiell@...cast.net>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	josh@...htriplett.org, tglx@...utronix.de, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, laijs@...fujitsu.com, dipankar@...ibm.com
Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory
	barrier (v5)

On Tue, Jan 12, 2010 at 09:39:56PM -0800, Nicholas Miell wrote:
> On Tue, 2010-01-12 at 21:31 -0800, Paul E. McKenney wrote:
> > Why is it OK to ignore the developer's request for an expedited
> > membarrer()?  The guy who expected the syscall to complete in a few
> > microseconds might not be so happy to have it take many milliseconds.
> > By the same token, the guy who specified non-expedited so as to minimally
> > disturb other threads in the system might not be so happy to see them
> > all be IPIed for no good reason.  ;-)
> > 
> > 							Thanx, Paul
> 
> Because the behavior is still correct, even if it is slower than you'd
> expect. It doesn't really matter where the expedited flag goes, though,
> because every future kernel will understand it.

In a real-time application, no shortage of which run on Linux, "going
slower than you expect" is a bug, right?

							Thanx, Paul
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