On Thu, Oct 31, 2013 at 11:22:00AM +0100, Ingo Molnar wrote: > > * Neil Horman <nhor...@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 >
Thank you ingo, that fixed it. I'm trying some other variants of the csum algorithm that Doug and I discussed last night, but FWIW, the relative performance of the 4 test cases (base/prefetch/parallel/both) remains unchanged. I'm starting to feel like at this point, theres very little point in doing parallel alu operations (unless we can find a way to break the dependency on the carry flag, which is what I'm tinkering with now). Neil -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
