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Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory
 barrier
From: Steven Rostedt <rostedt@goodmis.org>
Reply-To: rostedt@goodmis.org
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Oleg Nesterov <oleg@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
       linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
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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