diff options
Diffstat (limited to 'openmp/runtime/src/kmp_lock.cpp')
| -rw-r--r-- | openmp/runtime/src/kmp_lock.cpp | 46 |
1 files changed, 43 insertions, 3 deletions
diff --git a/openmp/runtime/src/kmp_lock.cpp b/openmp/runtime/src/kmp_lock.cpp index 3f9382f0d8b..53f4d9847c2 100644 --- a/openmp/runtime/src/kmp_lock.cpp +++ b/openmp/runtime/src/kmp_lock.cpp @@ -113,11 +113,11 @@ __kmp_acquire_tas_lock_timed_template( kmp_tas_lock_t *lck, kmp_int32 gtid ) KMP_YIELD_SPIN( spins ); } + kmp_backoff_t backoff = __kmp_spin_backoff_params; while ( ( lck->lk.poll != KMP_LOCK_FREE(tas) ) || ( ! KMP_COMPARE_AND_STORE_ACQ32( & ( lck->lk.poll ), KMP_LOCK_FREE(tas), KMP_LOCK_BUSY(gtid+1, tas) ) ) ) { - // - // FIXME - use exponential backoff here - // + + __kmp_spin_backoff(&backoff); if ( TCR_4( __kmp_nth ) > ( __kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc ) ) { KMP_YIELD( TRUE ); @@ -3008,6 +3008,46 @@ __kmp_set_drdpa_lock_flags( kmp_drdpa_lock_t *lck, kmp_lock_flags_t flags ) lck->lk.flags = flags; } +// Time stamp counter +#if KMP_ARCH_X86 || KMP_ARCH_X86_64 +# define __kmp_tsc() __kmp_hardware_timestamp() +// Runtime's default backoff parameters +kmp_backoff_t __kmp_spin_backoff_params = { 1, 4096, 100 }; +#else +// Use nanoseconds for other platforms +extern kmp_uint64 __kmp_now_nsec(); +kmp_backoff_t __kmp_spin_backoff_params = { 1, 256, 100 }; +# define __kmp_tsc() __kmp_now_nsec() +#endif + +// A useful predicate for dealing with timestamps that may wrap. +// Is a before b? +// Since the timestamps may wrap, this is asking whether it's +// shorter to go clockwise from a to b around the clock-face, or anti-clockwise. +// Times where going clockwise is less distance than going anti-clockwise +// are in the future, others are in the past. +// e.g.) a = MAX-1, b = MAX+1 (=0), then a > b (true) does not mean a reached b +// whereas signed(a) = -2, signed(b) = 0 captures the actual difference +static inline bool before(kmp_uint64 a, kmp_uint64 b) +{ + return ((kmp_int64)b - (kmp_int64)a) > 0; +} + +// Truncated binary exponential backoff function +void +__kmp_spin_backoff(kmp_backoff_t *boff) +{ + // We could flatten this loop, but making it a nested loop gives better result. + kmp_uint32 i; + for (i = boff->step; i > 0; i--) { + kmp_uint64 goal = __kmp_tsc() + boff->min_tick; + do { + KMP_CPU_PAUSE(); + } while (before(__kmp_tsc(), goal)); + } + boff->step = (boff->step<<1 | 1) & (boff->max_backoff-1); +} + #if KMP_USE_DYNAMIC_LOCK // Direct lock initializers. It simply writes a tag to the low 8 bits of the lock word. |
