[PATCH] D17433: [ARM] fix initialization of PredictableSelectIsExpensive

[James Molloy via llvm-commits]

Hi all,

My twopenniworth on this: cortex-a15, a12, a17 and krait have been lazy and inherited all the behaviours of cortex-a9. Therefore it is fine to choose a behaviour for a9 that doesn't take into account those other cores. They can change if it's an issue for them.

I feel that this flag will cause improvements and regressions whatever way it is set. The only real way to do this is using PGO. Therefore I feel that it should be set to whatever the most appropriate setting is for the core without real regard to benchmark results. Someone's going to be unhappy either way.

Just my 2c.

James

> On 23 Feb 2016, at 01:28, Junmo Park <junmoz.park at samsung.com> wrote:
>
> flyingforyou added a comment.
>
> Hi renato.
>
>> But I don't know how to measure the performance with test-suite.
>
>> If you know how to run the test-suite (http://llvm.org/docs/lnt/quickstart.html), you can just add the following options to lnt:
>
>
>> --threads=1 --build-threads=$CPUS --use-perf --benchmarking-only --multisample=8
>
>> Threads = 1 allows the benchmarking to be less noisy, built-threads should be on as much as the number of CPUs, use-perf if you have perf installed (linux-tools), the results are much more accurate, "benchmarking-only" is the key option here, which only runs the tests that are marked as benchmarks and multisample will run the same benchmarks N times (for ARM, you should run at least 3, but 5 is a good number, and 8 a better one).
>
>
> Oh.. What I wanted to say is that I don't know how to run test-suite on Apple devices. I have iPhone6S, 6, 5, mac mini. But I don't know how to run benchmarks/test-suite on these devices.
> Anyway, I really appreciate your detailed comments. Thanks. :)
>
>> You run the benchmarks on A53/57. Feel free to run EEMBC or SPEC, if you have access, too.
>
>
> Cortex-a53/57 didn't set schedule model. So, they don't have to be tested. Because the default setting for `PredictableSelectIsExpensive` is false.
> If I misunderstand about this, please let me know.
>
> Junmo.
>
>
> http://reviews.llvm.org/D17433
>
>
>
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