diff --git a/Python/lock.c b/Python/lock.c index ad97bfd93c8495..03bdc21b70f230 100644 --- a/Python/lock.c +++ b/Python/lock.c @@ -27,8 +27,10 @@ static const PyTime_t TIME_TO_BE_FAIR_NS = 1000*1000; // enabled. #if Py_GIL_DISABLED static const int MAX_SPIN_COUNT = 40; +static const int RELOAD_SPIN_COUNT = 3; #else static const int MAX_SPIN_COUNT = 0; +static const int RELOAD_SPIN_COUNT = 1; #endif struct mutex_entry { @@ -79,6 +81,16 @@ _PyMutex_LockTimed(PyMutex *m, PyTime_t timeout, _PyLockFlags flags) }; Py_ssize_t spin_count = 0; +#ifdef Py_GIL_DISABLED + // Using thread-id as a way of reducing contention further in the reload below. + // It adds a pseudo-random starting offset to the recurrence, so that threads + // are less likely to try and run compare-exchange at the same time. + // The lower bits of platform thread ids are likely to not be random, + // hence the right shift. + const Py_ssize_t tid = (Py_ssize_t) _Py_ThreadId() >> 12; +#else + const Py_ssize_t tid = 0; +#endif for (;;) { if ((v & _Py_LOCKED) == 0) { // The lock is unlocked. Try to grab it. @@ -92,6 +104,9 @@ _PyMutex_LockTimed(PyMutex *m, PyTime_t timeout, _PyLockFlags flags) // Spin for a bit. _Py_yield(); spin_count++; + if (((spin_count + tid) & RELOAD_SPIN_COUNT) == 0) { + v = _Py_atomic_load_uint8_relaxed(&m->_bits); + } continue; }