Messages in this thread | | | Date | Thu, 10 Apr 2014 09:44:30 -0500 | From | Clark Williams <> | Subject | Re: [RFC PATCH RT] rwsem: The return of multi-reader PI rwsems |
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On Wed, 9 Apr 2014 15:19:22 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> This patch is built on top of the two other patches that I posted > earlier, which should not be as controversial. > > If you have any benchmark on large machines I would be very happy if > you could test this patch against the unpatched version of -rt. > > Cheers, > > -- Steve >
Steven
I wrote a program named whack_mmap_sem which creates a large (4GB) buffer, then creates 2 x ncpus threads that are affined across all the available cpus. These threads then randomly write into the buffer, which should cause page faults galore.
I then built the following kernel configs:
vanilla-3.13.15 - no RT patches applied rt-3.12.15 - PREEMPT_RT patchset rt-3.12.15-fixes - PREEMPT_RT + rwsem fixes rt-3.12.15-multi - PREEMPT_RT + rwsem fixes + rwsem-multi patch
My test h/w was a Dell R520 with a 6-core Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz (hyperthreaded). So whack_mmap_sem created 24 threads which all partied in the 4GB address range.
I ran whack_mmap_sem with the argument -w 100000 which means each thread does 100k writes to random locations inside the buffer and then did five runs per each kernel. At the end of the run whack_mmap_sem prints out the time of the run in microseconds.
The means of each group of five test runs are:
vanilla.log: 1210117 rt.log: 17210953 (14.2 x slower than vanilla) rt-fixes.log: 10062027 (8.3 x slower than vanilla) rt-multi.log: 3179582 (2.x x slower than vanilla)
As expected, vanilla kicked RT's butt when hammering on the mmap_sem. But somewhat unexpectedly, your fixups helped quite a bit and the multi+fixups got RT back into being almost respectable.
Obviously these are just preliminary results on one piece of h/w but it looks promising.
Clark
P.S. If you want the source to whack_mmap_sem you can grab it from http://people.redhat.com/williams/whack_mmap_sem. If it looks like its worth keeping around I can add it to rt-tests.
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