Date: Mon, 1 Aug 2016 09:38:09 -0700 From: Maxim Sobolev <sobomax@freebsd.org> To: Mateusz Guzik <mjguzik@gmail.com>, Adrian Chadd <adrian.chadd@gmail.com>, John Baldwin <jhb@freebsd.org>, freebsd-current <freebsd-current@freebsd.org>, Konstantin Belousov <kib@freebsd.org> Subject: Re: [PATCH] randomized delay in locking primitives, take 2 Message-ID: <CAH7qZfuX339SoL1eaRvzMCGLP4WWHstq=PLNUpZKzXj3LnznZg@mail.gmail.com> In-Reply-To: <20160731203612.GH9408@dft-labs.eu> References: <20160731095706.GB9408@dft-labs.eu> <CAJ-VmokxFFe4iAuMKEZuCjua4YUHx=PiXJKSBibsDKxWOrm7uA@mail.gmail.com> <20160731203612.GH9408@dft-labs.eu>
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On Sun, Jul 31, 2016 at 1:36 PM, Mateusz Guzik <mjguzik@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. -Maxim
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