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

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Message-ID: <20100121170215.GC15761@Krystal>
Date:	Thu, 21 Jan 2010 12:02:15 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>, 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)

* Steven Rostedt (rostedt@...dmis.org) wrote:
> On Thu, 2010-01-21 at 11:22 -0500, Mathieu Desnoyers wrote:
> > * Steven Rostedt (rostedt@...dmis.org) wrote:
> 
> > > You may also need spin_lock_irqsave, et al. variants too.
> > 
> > Yep, or we simply use the local_irq_save/restore separately. That could
> > be a good idea given that only few specialized sites are affected.
> 
> If it gets used more often, then we need to consider RT. RT modifies
> spin_lock_irqsave into a standard mutex that does not disable
> interrupts. But if something does:
> 
> 	local_irq_save(flags);
> 	spin_lock_mb(&lock);
> 	[...]
> 
> Then it will break RT (if lock is to be converted).

Good point !

Mathieu

> 
> -- Steve
> 
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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