Messages in this thread |  | | | Date | Thu, 7 Jan 2010 08:52:49 -0800 | | From | "Paul E. McKenney" <> | | Subject | Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier |
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On Thu, Jan 07, 2010 at 09:44:15AM +0100, Peter Zijlstra wrote: > On Wed, 2010-01-06 at 22:35 -0800, Josh Triplett wrote: > > > > The number of threads doesn't matter nearly as much as the number of > > threads typically running at a time compared to the number of > > processors. Of course, we can't measure that as easily, but I don't > > know that your proposed heuristic would approximate it well. > > Quite agreed, and not disturbing RT tasks is even more important.
OK, so I stand un-Reviewed-by twice in one morning. ;-)
> A simple: > > for_each_cpu(cpu, current->mm->cpu_vm_mask) { > if (cpu_curr(cpu)->mm == current->mm) > smp_call_function_single(cpu, func, NULL, 1); > } > > seems far preferable over anything else, if you really want you can use > a cpumask to copy cpu_vm_mask in and unset bits and use the mask with > smp_call_function_any(), but that includes having to allocate the > cpumask, which might or might not be too expensive for Mathieu.
This would be vulnerable to the sys_membarrier() CPU seeing an old value of cpu_curr(cpu)->mm, and that other task seeing the old value of the pointer we are trying to RCU-destroy, right?
Thanx, Paul
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