On 10 May 2016 at 19:18, Ilya Verbin <iver...@gmail.com> wrote:
> On Tue, May 10, 2016 at 14:36:36 +0100, Ramana Radhakrishnan wrote:
>> On Tue, May 10, 2016 at 2:02 PM, Christophe Lyon
>> <christophe.l...@linaro.org> wrote:
>> > On 9 May 2016 at 15:34, Christophe Lyon <christophe.l...@linaro.org> wrote:
>> >> On 9 May 2016 at 15:29, Jeff Law <l...@redhat.com> wrote:
>> >>> On 05/09/2016 01:37 AM, Christophe Lyon wrote:
>> >>>> After this merge, I'm seeing lots of timeouts on arm (using QEMU).
>> >>>> Is this "expected"? (as in: should I increase my timeout value)
>> >>>
>> >>> I wouldn't say it's expected; this is the first time Cilk+ has been
>> >>> supported on ARM. It could be a bug in the ARM support in the runtime,
>> >>> an
>> >>> ARM compiler bug or even a bug in the ARM QEMU support.
>> >>>
>> >>> Probably the first step is to see if it's working properly on real
>> >>> hardware.
>> >>> That would at least allow us to eliminate QEMU from the equation if it's
>> >>> failing in the same manner on a real machine.
>> >>>
>> >> OK, I'll check that.
>> >> I wanted to know if I was missing something obvious.
>> >
>> > I've tested in an armhf chroot on an armv8 machine, and I saw SIGILL errors
>> > on:
>> > mcr 15, 0, r3, cr7, cr10, {4}
>> > which is how __cilkrts_fence is implemented in
>> > ../libcilkrts/runtime/config/arm/os-fence.h
>>
>> At first glance I'd ask why this shouldn't be __atomic_thread_fence or
>> __atomic_signal_fence ( SEQ_CST) if that's what they want here and
>> then it will work (TM) regardless of architecture levels.
>>
>> > This instruction is not supported anymore on armv8. Recent arm64 kernels
>> > have handlers for it.
>> >
>> > So we may want the implementation to be conditional, or prefer to rely on
>> > kernel support.
>
> ARM enabling code was taken from community contribution, we haven't tested it.
> If someone wants to fix this, it would be appreciated.
>
Following Ramana's suggestion, I tried:
# define __cilkrts_fence() __atomic_thread_fence(__ATOMIC_SEQ_CST);
and the tests now pass.
Christophe
> Thanks,
> -- Ilya
