Thanks Jim, When I uses "-mtune and/or -mcpu" with GCC6.2 then I see almost same number as with GC4.9
Thanks -Bharat On 7 February 2017 at 23:37, Jim Wilson <jim.wil...@linaro.org> wrote: > On Tue, Feb 7, 2017 at 7:50 AM, Bharat Bhushan > <bharat.bhus...@linaro.org> wrote: > > I am working on log10/qsort benchmarks on ARM64 (ARMv8) processor, > > I want to check if we have experience with these benchmarks. > > We have experience with things like SPEC and Coremark, which are > compiler performance benchmarks. log10/qsort sounds like glibc > functions. Are you testing glibc performance? That would perhaps > depend more on the glibc version than the compiler version. > > > Actually i am looking for a compiler version which gives best results > with > > these benchmarks and specific compiler optimization (in my case is see O3 > > gives best numbers) ? > > What exactly are you trying to optimize? If you want best performance > for your application, then you try every compiler version and every > option and use the combination that gives the best performance. Us > toolchain developers only care about performance of the latest > version, and if it isn't the best performing one, then we try to fix > it. If you want best performance for the most people, then you > concentrate on -O2 results as that is what most people use. I can't > give a better answer without more specifics of what exactly you are > trying to do. > > > I have tried GCC-4.9 and GCC-6.2 with log10 benchmark and my observations > > are: > > 1) With gcc 4.9 - 140 us > > 2) With GCC 6.2 - 150 us > > My compilation flags are "-O3 -ftree-vectorize -funroll-all-loops --param > > max-inline-insns-auto=550 --param case-values-threshold=30 > > -falign-functions=32 -ftracer" > > > > So it seems like gcc-6.2 is better, am i missing something, should i use > > some better compiler flags? > > Usually for benchmarks, a faster runtime is a better result, so it > looks like gcc-4.9 is giving the better result. If that is a gcc-6 > bug, then it should be reported so we can try to fix it. However, you > are using a lot of options, and some of those options aren't the > default because they don't always give the best results. The > usefulness of some uncommon optimization options can vary from one gcc > release to the next. You may need to use different sets of gcc > options with different gcc versions to get the best results. But > again, as mentioned above, this all depends on what exactly you are > trying to do, and you haven't given us enough info to understand that. > > Jim >
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