[Openmp-dev] Enabling OMPT by default

Wed Dec 20 01:16:49 PST 2017

> I think we don't have access to an ARM machine to test ourselves
There was someone on Twitter the other day running OpenMP code on his Raspberry Pi (using "Raspbian", 
I assume since he had a Linux environment) so it may be possible to add ARM to your testing environment
at little monetary cost. (Of course the time cost to get it all working may be non-trivial, but the
 hardware cost seems under 100Euro).

That would be a 32bit ARM, not AARCH64, but still better than nothing.

-- Jim

Jim Cownie <james.h.cownie at intel.com>
SSG/DPD/TCAR (Technical Computing, Analyzers, and Runtimes)
Tel: +44 117 9071438

-----Original Message-----
From: Openmp-dev [mailto:openmp-dev-bounces at lists.llvm.org] On Behalf Of Jonas Hahnfeld via Openmp-dev
Sent: Tuesday, December 19, 2017 6:52 PM
To: Paul Osmialowski <pawel.osmialowski at foss.arm.com>
Cc: openmp-dev at lists.llvm.org
Subject: Re: [Openmp-dev] Enabling OMPT by default

Am 2017-12-19 15:15, schrieb Paul Osmialowski:
> Nah, it blocks forever on nested_lwt.c when I started it on 96-cores
> ARMv8.1 machine.

Can you get us a stack trace? I think we don't have access to an ARM 
machine to test ourselves but we might be able to guess based on the 
implementation.

> BTW, the missing part of callbacks.h for tests I added like this:
> 
> diff --git a/runtime/test/ompt/callback.h 
> b/runtime/test/ompt/callback.h
> index 8481fb4..9a560aa 100755
> --- a/runtime/test/ompt/callback.h
> +++ b/runtime/test/ompt/callback.h
> @@ -105,6 +105,11 @@ ompt_label_##id:
>  #define print_possible_return_addresses(addr) \
>    printf("%" PRIu64 ": current_address=%p\n", 
> ompt_get_thread_data()->value, \
>           ((char *)addr) - 8)
> +#elif KMP_ARCH_AARCH64
> +// On AArch64 the NOP instruction is 4 bytes long.
> +#define print_possible_return_addresses(addr) \
> +  printf("%" PRIu64 ": current_address=%p\n", 
> ompt_get_thread_data()->value, \
> +         ((char *)addr) - 4)
>  #else
>  #error Unsupported target architecture, cannot determine address 
> offset!
>  #endif

Interesting that we don't have a load instruction at all for AArch64. 
Sigh, that's why we have to customize it for every architecture...

> 
> On 18/12/2017 13:56, Jonas Hahnfeld via Openmp-dev wrote:
>> Does it pass the tests? I doubt that because it needs modifications as 
>> Joachim pointed out (had to do the same for PPC64).
>> 
>> Jonas
>> 
>> Am 2017-12-18 14:52, schrieb Pawel Osmialowski:
>>> Guys,
>>> 
>>> For more than a year I was always building libomp with
>>> -DLIBOMP_OMPT_SUPPORT=ON for our AArch64 machines and I'd happily see
>>> it enabled by default.
>>> 
>>> Cheers,
>>> Paul
>>> 
>>> 
>>> On Mon, 2017-12-18 at 14:23 +0100, Jonas Hahnfeld wrote:
>>>> Adding Paul, maybe he can help here. Though switching the default
>>>> for
>>>> x86/x86_64 and ppc64 doesn't mean it has to work on AArch64 for the
>>>> 6.0
>>>> release, it will just stay deactivated as for MIPS(64).
>>>> 
>>>> Jonas
>>>> 
>>>> Am 2017-12-18 13:02, schrieb Cownie, James H via Openmp-dev:
>>>> > The ARM folks should chip in. This should clearly be tested on
>>>> > AARCH64
>>>> > as well!
>>>> >
>>>> > -- Jim
>>>> >
>>>> > Jim Cownie <james.h.cownie at intel.com>
>>>> > SSG/DPD/TCAR (Technical Computing, Analyzers, and Runtimes)
>>>> > Tel: +44 117 9071438
>>>> >
>>>> > -----Original Message-----
>>>> > From: Openmp-dev [mailto:openmp-dev-bounces at lists.llvm.org] On
>>>> > Behalf
>>>> > Of Joachim Protze via Openmp-dev
>>>> > Sent: Monday, December 18, 2017 11:58 AM
>>>> > To: Openmp-dev <openmp-dev at lists.llvm.org>
>>>> > Subject: [Openmp-dev] Enabling OMPT by default
>>>> >
>>>> > Dear all,
>>>> >
>>>> > OpenMP 5.0 will introduce OMPT, the OpenMP tools interface. The
>>>> > current
>>>> > implementation in the LLVM/OpenMP runtime is at the level of
>>>> > OpenMP
>>>> > TR6,
>>>> > as published in November (with some known issues, were we have
>>>> > patches
>>>> > under review).
>>>> > Currently, this feature is deactivated by default
>>>> > (LIBOMP_OMPT_SUPPORT).
>>>> > According to overhead measurements performed by Intel and on some
>>>> > of
>>>> > our
>>>> > machines, this feature introduces a worst case runtime overhead of
>>>> > ~4%,
>>>> > but for most cases basically no overhead.
>>>> > As I understood, some of the build-bots run the tests when the
>>>> > feature
>>>> > is enabled. We locally test the changes continuously with different
>>>> > compiler versions (icc/gcc/clang), but only on x86_64 architecture.
>>>> > Further, this feature was tested on ppc64.
>>>> >
>>>> > How should we proceed to enable this feature by default, and get it
>>>> > tested on other architectures?
>>>> > For the 6.0 release, I would like to enable OMPT at least for the
>>>> > supported platforms x86/x86_64 and ppc64.
>>>> >
>>>> >
>>>> > We would also appreciate collaboration with vendors/users of other
>>>> > platforms, to ensure the code is running there.
>>>> >
>>>> > Typically, only the architecture specific offset needs to be added:
>>>> > https://github.com/llvm-mirror/openmp/blob/master/runtime/test/ompt
>>>> > /callback.h#L95
>>>> >
>>>> > Looking forward to your feedback,
>>>> >
>>>> > Joachim
>>>> > _______________________________________________
>>>> > Openmp-dev mailing list
>>>> > Openmp-dev at lists.llvm.org
>>>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
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