128-bit CAS without Assembly Broken?

[nmhamster]

If I comment out the assembly version of the 128-bit CAS loop and compile with OpenMP tests fail on X86 systems with GNU and Intel. Not sure but the fall-back may be broken which could have impact on other platforms.

[crtrott]

Ok I think this was only in pull request #160

The problem is that the use of cas128 was only protected by "if defined(KOKKOS_ENABLE_ASM)" while the contents of cas128 with the changes in the pull request were now protected by
"if defined(KOKKOS_ENABLE_ASM) && defined ( KOKKOS_USE_ISA_X86_64 )".
That way the 128 cas which got called was actually not atomic, which made the tests fail since the cas loops never finished.
I changed it so that the whole function is not visible anymore (not just the loop body) if those two things are not defined, and I protected the use of cas128 with both defines everywhere.

So now if either KOKKOS_ENABLE_ASM or KOKKOS_USE_ISA_X86_64 is not defined 128 bit atomics go to the generic backend.

[nmhamster]

?Great thanks!

S.

Simon Hammond
Center for Computing Research (Scalable Computer Architectures)
Sandia National Laboratories, NM
[Sent from remote connection, please excuse typing errors]

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From: Christian Trott notifications@github.com
Sent: Saturday, December 19, 2015 3:36 PM
To: kokkos/kokkos
Cc: Hammond, Simon David (-EXP)
Subject: [EXTERNAL] Re: [kokkos] 128-bit CAS without Assembly Broken? (#161)

Ok I think this was only in pull request #160#160

The problem is that the use of cas128 was only protected by "if defined(KOKKOS_ENABLE_ASM)" while the contents of cas128 with the changes in the pull request were now protected by
"if defined(KOKKOS_ENABLE_ASM) && defined ( KOKKOS_USE_ISA_X86_64 )".
That way the 128 cas which got called was actually not atomic, which made the tests fail since the cas loops never finished.
I changed it so that the whole function is not visible anymore (not just the loop body) if those two things are not defined, and I protected the use of cas128 with both defines everywhere.

So now if either KOKKOS_ENABLE_ASM or KOKKOS_USE_ISA_X86_64 is not defined 128 bit atomics go to the generic backend.

Reply to this email directly or view it on GitHubhttps://github.com//issues/161#issuecomment-166031241.