This commit disables the use of both the builtin and hand-written
atomics if proper C11 atomic support is detected. This is the first
step towards requiring the availability of C11 atomics for the C
compiler used to build Open MPI.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
This commit updates the entire codebase to use specific opal types for
all atomic variables. This is a change from the prior atomic support
which required the use of the volatile keyword. This is the first step
towards implementing support for C11 atomics as that interface
requires the use of types declared with the _Atomic keyword.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
This commit updates the atomic fifo code to fix a consistency issue
observed on Power9 systems when builtin atomics are used. The cause
was two things: 1) a missing write memory barrier in fifo push, and 2)
a read ordering issue when reading the fifo head non-atomically. This
commit fixes both issues and appears to correct then inconsistency.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
This commit fixes a hang that occurs with debug builds of Open MPI on
aarch64 and power/powerpc systems. When the ll/sc atomics are inline
functions the compiler emits load/store instructions for the function
arguments with -O0. These extra load/store arguments can cause the ll
reservation to be cancelled causing live-lock.
Note that we did attempt to fix this with always_inline but the extra
instructions are stil emitted by the compiler (gcc). There may be
another fix but this has been tested and is working well.
References #3697. Close when applied to v3.0.x and v3.1.x.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
This commit adds a new set of compare-and-exchange functions. These
functions have a signature similar to the functions found in C11. The
old cmpset functions are now deprecated and defined in terms of the
new compare-and-exchange functions. All asm backends have been
updated.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
This commit renames the atomic compare-and-swap functions to indicate
the return value. This is in preperation for adding support for a
compare-and-swap that returns the old value. At the same time the
return type has been changed to bool.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
This commit changes the opal_fifo_push code to use
opal_update_counted_pointer to set the head. This fixes a data race
that occurs because the read of the fifo head in opal_fifo_pop
requires two instructions. This combined with the non-atomic update in
opal_fifo_push can lead to an ABA issue that puts the fifo in an
inconsistant state.
There are other ways this problem could be fixed. One way would be to
introduce an opal_atomic_read_128 implementation. On x86_64 this would
have to use the cmpxchg16b instruction. Since this instruction would
have to be in the pop path (and always executed) it would be slower
than the fix in this commit.
Closesopen-mpi/ompi#1460.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
This commit adds a new class: opal_fifo.h. The new class has atomic, non-atomic,
and opal_using_threads() conditoned routines. It should be used when first-in
first-out is required and should perform much better than using locks and an
opal_list_t. Like with opal_lifo_t there are two versions of the atomic
implementation: 128-bit compare-and-swap, and spin-locked. More implementations
can be added later (LL/SC comes to mind).
This commit also adds a unit test for the opal_fifo_t class. This test verifies
the fifo implementation when using multiple threads.
