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

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Date:	Sat, 9 Jan 2010 20:04:51 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Steven Rostedt <rostedt@...dmis.org>
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

* Steven Rostedt (rostedt@...dmis.org) wrote:
> 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;

This is not required with for_each_cpu(cpu, mm_cpumask(current->mm)),
because it only iterates on active cpus on which the current process
threads are scheduled.

Thanks,

Mathieu

> 
> > 	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
> 
> 

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