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

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Date:	Sat, 09 Jan 2010 18:16:40 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.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

On Sat, 2010-01-09 at 18:05 -0500, Steven Rostedt wrote:

> Then we should have O(tasks) for spinlocks taken, and 
> O(min(tasks, CPUS)) for IPIs.
> 

And for nr tasks >> CPUS, this may help too:

> cpumask = 0;
> foreach task {

	if (cpumask == online_cpus)
		break;

> 	spin_lock(task_rq(task)->rq->lock);
> 	if (task_rq(task)->curr == task)
> 		cpu_set(task_cpu(task), cpumask);
> 	spin_unlock(task_rq(task)->rq->lock);
> }
> send_ipi(cpumask);
> 

-- Steve


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