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PyMutex is a one byte lock with fast, inlineable lock and unlock functions for the common uncontended case. The design is based on WebKit's WTF::Lock. PyMutex is built using the _PyParkingLot APIs, which provides a cross-platform futex-like API (based on WebKit's WTF::ParkingLot). This internal API will be used for building other synchronization primitives used to implement PEP 703, such as one-time initialization and events. This also includes tests and a mini benchmark in Tools/lockbench/lockbench.py to compare with the existing PyThread_type_lock. Uncontended acquisition + release: * Linux (x86-64): PyMutex: 11 ns, PyThread_type_lock: 44 ns * macOS (arm64): PyMutex: 13 ns, PyThread_type_lock: 18 ns * Windows (x86-64): PyMutex: 13 ns, PyThread_type_lock: 38 ns PR Overview: The primary purpose of this PR is to implement PyMutex, but there are a number of support pieces (described below). * PyMutex: A 1-byte lock that doesn't require memory allocation to initialize and is generally faster than the existing PyThread_type_lock. The API is internal only for now. * _PyParking_Lot: A futex-like API based on the API of the same name in WebKit. Used to implement PyMutex. * _PyRawMutex: A word sized lock used to implement _PyParking_Lot. * PyEvent: A one time event. This was used a bunch in the "nogil" fork and is useful for testing the PyMutex implementation, so I've included it as part of the PR. * pycore_llist.h: Defines common operations on doubly-linked list. Not strictly necessary (could do the list operations manually), but they come up frequently in the "nogil" fork. ( Similar to https://man.freebsd.org/cgi/man.cgi?queue) --------- Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>
53 lines
2 KiB
Python
53 lines
2 KiB
Python
# Measure the performance of PyMutex and PyThread_type_lock locks
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# with short critical sections.
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#
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# Usage: python Tools/lockbench/lockbench.py [CRITICAL_SECTION_LENGTH]
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#
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# How to interpret the results:
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#
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# Acquisitions (kHz): Reports the total number of lock acquisitions in
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# thousands of acquisitions per second. This is the most important metric,
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# particularly for the 1 thread case because even in multithreaded programs,
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# most locks acquisitions are not contended. Values for 2+ threads are
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# only meaningful for `--disable-gil` builds, because the GIL prevents most
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# situations where there is lock contention with short critical sections.
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#
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# Fairness: A measure of how evenly the lock acquisitions are distributed.
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# A fairness of 1.0 means that all threads acquired the lock the same number
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# of times. A fairness of 1/N means that only one thread ever acquired the
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# lock.
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# See https://en.wikipedia.org/wiki/Fairness_measure#Jain's_fairness_index
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from _testinternalcapi import benchmark_locks
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import sys
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# Max number of threads to test
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MAX_THREADS = 10
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# How much "work" to do while holding the lock
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CRITICAL_SECTION_LENGTH = 1
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def jains_fairness(values):
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# Jain's fairness index
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# See https://en.wikipedia.org/wiki/Fairness_measure
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return (sum(values) ** 2) / (len(values) * sum(x ** 2 for x in values))
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def main():
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print("Lock Type Threads Acquisitions (kHz) Fairness")
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for lock_type in ["PyMutex", "PyThread_type_lock"]:
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use_pymutex = (lock_type == "PyMutex")
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for num_threads in range(1, MAX_THREADS + 1):
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acquisitions, thread_iters = benchmark_locks(
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num_threads, use_pymutex, CRITICAL_SECTION_LENGTH)
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acquisitions /= 1000 # report in kHz for readability
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fairness = jains_fairness(thread_iters)
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print(f"{lock_type: <20}{num_threads: <18}{acquisitions: >5.0f}{fairness: >20.2f}")
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if __name__ == "__main__":
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if len(sys.argv) > 1:
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CRITICAL_SECTION_LENGTH = int(sys.argv[1])
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main()
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