Messages in this thread | | | Date | Thu, 31 Oct 2013 11:22:00 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's |
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* Neil Horman <nhorman@tuxdriver.com> wrote:
> > etc. For such short runtimes make sure the last column displays > > close to 100%, so that the PMU results become trustable. > > > > A nehalem+ PMU will allow 2-4 events to be measured in parallel, > > plus generics like 'cycles', 'instructions' can be added 'for free' > > because they get counted in a separate (fixed purpose) PMU register. > > > > The last colum tells you what percentage of the runtime that > > particular event was actually active. 100% (or empty last column) > > means it was active all the time. > > > > Thanks, > > > > Ingo > > > > Hmm, > > I ran this test: > > for i in `seq 0 1 3` > do > echo $i > /sys/module/csum_test/parameters/module_test_mode > taskset -c 0 perf stat --repeat 20 -C 0 -e L1-dcache-load-misses -e L1-dcache-prefetches -e cycles -e instructions -ddd ./test.sh > done
You need to remove '-ddd' which is a shortcut for a ton of useful events, but here you want to use fewer events, to increase the precision of the measurement.
Thanks,
Ingo
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