Jes Sorensen wrote:
I'm a little wary of the performance impact of this change. Doing a cpumask compare on all smp_call_function calls seems a little expensive. Maybe it's just noise in the big picture compared to the actual cost of the IPIs, but I thought I'd bring it up. Keep in mind that a cpumask can be fairly big these days, max NR_CPUS is currently 4096. For those booting a kernel with NR_CPUS at 4096 on a dual CPU machine, it would be a bit expensive.
Unless your hardware has remarkably fast IPIs, I think really the cost of scanning 512 bytes is going to be in the noise...
This change has been on the x86 side for ages, and not even Ingo made a peep about it ;)
Why not keep smp_call_function() the way it was before, rather than implementing it via the call to smp_call_function_mask()?
Because Xen needs a different core implementation (because of its different IPI implementation), and it would be better to just have to do one of them rather than N.
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