Messages in this thread | | | Date | Thu, 7 Jan 2010 10:07:58 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier |
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* Peter Zijlstra (peterz@infradead.org) 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. > > 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. >
I like this ! :)
Following some testing, I think I'll go with your scheme, with 2 smp_call_function_single (one function call for the local thread, one IPI). If we need more than that, then we allocate a cpumask and call smp_call_function_many() for the other cpus. I provide benchmarks in my reply to Josh justifying this choice.
Thanks,
Mathieu
-- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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