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

Steven Rostedt
2010-01-07T14:27:43Z

On Thu, 2010-01-07 at 01:19 -0500, Mathieu Desnoyers wrote:

> I see your point.

Actually you are missing the point ;-)

>
> This would probably be good for machines with very large number of cpus
> and without IPI broadcast support, running processes with only few
> threads. I really start to think that we should have some way to compare
> the number of threads belonging to a process and choose between the
> broadcast IPI and the per-cpu IPI depending if we are over or under an
> arbitrary threshold.

This has nothing to do with performance. It has to do with a thread
should not interfere with a thread belonging to another process. We
really don't care how long the sys_membarrier() takes (it's the slow
path anyway). We do care that a critical RT task is being interrupted by
some java thread sending thousands of IPIs.

-- Steve