[PATCH] randomized delay in locking primitives, take 2

Maxim Sobolev sobomax at freebsd.org
Mon Aug 1 16:38:11 UTC 2016

On Sun, Jul 31, 2016 at 1:36 PM, Mateusz Guzik <mjguzik at gmail.com> wrote:

> On Sun, Jul 31, 2016 at 07:03:08AM -0700, Adrian Chadd wrote:
> > Hi,
> >
> > Did you test on any 1, 2, 4, 8 cpu machines? just to see if there are
> > any performance degredations on lower count CPUs?
> >
> I did not test on machines which physically that few cpus, but I did
> test the impact on microbenchmark with 2 and 4 threads on the 80-way
> machine. There was no difference.

Well, arguably running 4 threads on a 80-way machine is not quite the same
as running the same 4 threads on 4-way or 8-way machine. Unless you
actually bind your test threads to a specific CPUs, on a bigger system
scheduler is free to migrate your thread on another CPU if all 4 are
spinning, this might not the option for smaller box. I suggest you at very
least re-run your benchmark on a virtual machine with small CPUs count
assigned, it should be quite easy to do so on your monster box.


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