[Bug 243212] High CPU usage when set affinity on multiple CPU

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=243212

Mark Johnston <markj at FreeBSD.org> changed:

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                 CC|                            |markj at FreeBSD.org

--- Comment #2 from Mark Johnston <markj at FreeBSD.org> ---
> I guess that this regression has something to do with NUMA, maybe threads 4,5 are forced to use memory domain 0, causing the additional CPU usage.

The policy as reported by cpuset is first-touch, meaning that threads will
attempt to allocate memory from the local domain first.

Some things you could try to help narrow the problem down:
- Look at memory utilization.  Do you have lots of free memory in both domains?
- Collect a flamegraph using https://github.com/brendangregg/FlameGraph to see
where the high system CPU time is coming from.
- Try other domain allocation policies.  round-robin will cause threads to
alternate between the two domains.  You can also try forcing all allocations to
come from domain 0, where most of the threads are running.
- Try disabling thread pinning.
- Try setting the vm.numa.disabled tunable to 1.  I think this will force the
page allocator to behave the same as it would in 11.3, so you can rule out
other differences between 11.3 and 12.1 that might be causing a problem.

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