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Demonstrate some ways to improve WITH-MUTEX
We can get at least 25% speedup by eschewing all the async unwind crap. There's also some improvement possible by using the mutex3 algorithm from the "Futexes are Tricky" paper. These tests also show that it is theoretically possible to retain synchronous NLX safety by chaining all owned mutexes onto a dynamic-extent list; when unwinding the binding stack due to NLX we would just need to release each held mutex. As to async unwind safety, it is mostly unreliable garbage anyway, and nobody should need it in production code. Performance would presumably not be a concern for a subset of users. It's just a question of how to convert from the old API to a new one that does not promise asynchronous interrupt safety where users have come to expect it.
This commit is contained in:
Douglas Katzman
parent
95e977a59b
commit
4b32a20109
208
benchmarks/grab-mutex.lisp
Normal file
208
benchmarks/grab-mutex.lisp
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@ -0,0 +1,208 @@
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(in-package sb-thread)
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(sb-ext:defglobal *mutex* (sb-thread:make-mutex))
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(declaim (type mutex *mutex*))
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(sb-ext:defglobal *start-semaphore* nil)
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(sb-ext:defglobal *ready-semaphore* nil)
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(defmacro timing (&body body)
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`(binding* ((start-real (get-internal-real-time))
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((thread-start-sec thread-start-nsec)
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(sb-unix::clock-gettime sb-unix:clock-thread-cputime-id)))
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,@body
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(binding* ((stop-real (get-internal-real-time))
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((thread-stop-sec thread-stop-nsec)
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(sb-unix::clock-gettime sb-unix:clock-thread-cputime-id)))
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(values (- stop-real start-real) ; microseconds
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(+ (* 1000000 (- thread-stop-sec thread-start-sec))
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(round (- thread-stop-nsec thread-start-nsec) 1000))))))
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(defmacro timing-test (&body body)
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`(let ((m *mutex*) (waste (make-array 100 :element-type 'sb-vm:word)))
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(declare (truly-dynamic-extent waste))
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(setq sb-thread::*grab-mutex-calls-performed* 0)
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;; Get all threads to agree on the moment they should start
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(sb-thread:signal-semaphore *ready-semaphore*)
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(sb-thread:wait-on-semaphore *start-semaphore*)
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(macrolet ((do-some-work ()
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;; Perform a slightly nontrivial amount of "stuff"
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;; i.e. more than just assigning a variable.
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'(dotimes (i (length waste))
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(setf (aref waste i) (logxor (aref waste i) (ash 1 (mod i 64)))))))
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(timing ,@body))))
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;;; Default implementation of WITH-MUTEX
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(defun grab-and-release-baseline-nlx-protected (n-iter)
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(timing-test
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(dotimes (i (the fixnum n-iter))
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(sb-thread:with-mutex (m)
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(do-some-work)))))
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;;; Default implementation of grab/release but no interrupt-safety
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(defun grab-and-release-baseline-unprotected (n-iter)
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(timing-test
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(dotimes (i (the fixnum n-iter))
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(sb-thread:grab-mutex m)
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(do-some-work)
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(sb-thread:release-mutex m))))
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(defvar *mutexes-held* nil)
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(setf (sb-int:info :variable :wired-tls '*mutexes-held*) :always-thread-local
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(sb-int:info :variable :always-bound '*mutexes-held*) :always-bound)
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(defmacro binding-mutexes-held ((mutex) &body body)
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`(dx-let ((*mutexes-held* (cons ,mutex *mutexes-held*))) ,@body))
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;;; Faster implementation of grab and release
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(defun grab-and-release-algo-2 (n-iter)
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(timing-test
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(dotimes (i (the fixnum n-iter))
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(sb-thread:wait-for-mutex-algorithm-2 m)
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(binding-mutexes-held (m)
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(do-some-work)
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(sb-thread:fast-release-mutex m)))))
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;;; Faster implementation, and GRAB- can often avoid a function call
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(defun grab-and-release-algo-2+ (n-iter)
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(timing-test
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(dotimes (i (the fixnum n-iter))
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(sb-thread:wait-for-mutex-2-partial-inline m)
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(binding-mutexes-held (m)
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(do-some-work)
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(sb-thread:fast-release-mutex m)))))
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(defun grab-and-release-algo-3 (n-iter)
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(timing-test
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(dotimes (i (the fixnum n-iter))
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(sb-thread:wait-for-mutex-algorithm-3 m)
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(binding-mutexes-held (m)
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(do-some-work)
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(sb-thread:fast-release-mutex m)))))
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(defun grab-and-release-algo-3+ (n-iter)
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(timing-test
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(dotimes (i (the fixnum n-iter))
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(sb-thread:wait-for-mutex-3-partial-inline m)
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(binding-mutexes-held (m)
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(do-some-work)
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(sb-thread:fast-release-mutex m)))))
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(defun try (n-threads n-iter label testfun)
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(let (threads)
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(setq *ready-semaphore* (sb-thread:make-semaphore))
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(setq *start-semaphore* (sb-thread:make-semaphore))
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(dotimes (i n-threads)
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(push (sb-thread:make-thread testfun :arguments n-iter)
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threads))
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;; Wait until all threads say that they're ready
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(sb-thread:wait-on-semaphore *ready-semaphore* :n n-threads)
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;; "Unleash the hounds"
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(sb-thread:signal-semaphore *start-semaphore* n-threads)
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(let ((sum-real 0)
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(sum-cpu 0))
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(dolist (thread threads)
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(multiple-value-bind (realtime cputime)
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(sb-thread:join-thread thread)
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;;(format t "real: ~5d cpu: ~5d~%" realtime cputime)
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(incf sum-real realtime)
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(incf sum-cpu cputime)))
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(format t "~20a: cpu=(sum=~8d avg=~8d) real=~8d~@[ [~d calls]~]~%"
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label
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sum-cpu (floor sum-cpu n-threads)
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(floor sum-real n-threads)
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(let ((c sb-thread::*grab-mutex-calls-performed*))
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(unless (zerop c) c))))))
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(defun test-n-threads (n)
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(try n 100000 "WITH-MUTEX" 'grab-and-release-baseline-nlx-protected)
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(try n 100000 "GRAB+RELEASE" 'grab-and-release-baseline-unprotected)
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(try n 100000 "ALGO2" 'grab-and-release-algo-2)
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(try n 100000 "ALGO2+" 'grab-and-release-algo-2+)
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(try n 100000 "ALGO3" 'grab-and-release-algo-3)
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(try n 100000 "ALGO3+" 'grab-and-release-algo-3+))
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#|
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* (sb-thread::test-n-threads 5)
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WITH-MUTEX : cpu=(sum= 1129410 avg= 225882) real= 251198
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GRAB+RELEASE : cpu=(sum= 1013281 avg= 202656) real= 221599
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ALGO2 : cpu=(sum= 983301 avg= 196660) real= 217599 [480215 calls]
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ALGO2+ : cpu=(sum= 906144 avg= 181228) real= 199999 [240760 calls]
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ALGO3 : cpu=(sum= 953727 avg= 190745) real= 212000 [482759 calls]
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ALGO3+ : cpu=(sum= 893479 avg= 178695) real= 199998 [246538 calls]
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* (sb-thread::test-n-threads 10)
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WITH-MUTEX : cpu=(sum= 4744457 avg= 474445) real= 535597
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GRAB+RELEASE : cpu=(sum= 4854507 avg= 485450) real= 544798
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ALGO2 : cpu=(sum= 4168526 avg= 416852) real= 453997 [968121 calls]
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ALGO2+ : cpu=(sum= 3720948 avg= 372094) real= 409599 [462061 calls]
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ALGO3 : cpu=(sum= 4091659 avg= 409165) real= 444797 [970730 calls]
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ALGO3+ : cpu=(sum= 3824551 avg= 382455) real= 418398 [404065 calls]
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* (sb-thread::test-n-threads 15)
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WITH-MUTEX : cpu=(sum=12460694 avg= 830712) real= 909595
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GRAB+RELEASE : cpu=(sum=11579420 avg= 771961) real= 835462
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ALGO2 : cpu=(sum= 9343377 avg= 622891) real= 654131 [1463285 calls]
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ALGO2+ : cpu=(sum= 8908803 avg= 593920) real= 631996 [571894 calls]
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ALGO3 : cpu=(sum= 9262899 avg= 617526) real= 654929 [1458653 calls]
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ALGO3+ : cpu=(sum= 8771110 avg= 584740) real= 620264 [539979 calls]
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* (sb-thread::test-n-threads 20)
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WITH-MUTEX : cpu=(sum=18373401 avg= 918670) real= 1157394
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GRAB+RELEASE : cpu=(sum=19171438 avg= 958571) real= 1110394
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ALGO2 : cpu=(sum=15958082 avg= 797904) real= 883196 [1947759 calls]
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ALGO2+ : cpu=(sum=14531894 avg= 726594) real= 839596 [776184 calls]
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ALGO3 : cpu=(sum=16258896 avg= 812944) real= 869995 [1950461 calls]
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ALGO3+ : cpu=(sum=15892267 avg= 794613) real= 840197 [719736 calls]
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* (sb-thread::test-n-threads 25)
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WITH-MUTEX : cpu=(sum=24908201 avg= 996328) real= 1425273
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GRAB+RELEASE : cpu=(sum=24098405 avg= 963936) real= 1358552
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ALGO2 : cpu=(sum=18334699 avg= 733387) real= 1135194 [2402256 calls]
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ALGO2+ : cpu=(sum=18920912 avg= 756836) real= 1095675 [932165 calls]
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ALGO3 : cpu=(sum=20350344 avg= 814013) real= 1100794 [2427181 calls]
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ALGO3+ : cpu=(sum=19708020 avg= 788320) real= 1051835 [891826 calls]
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* (sb-thread::test-n-threads 30)
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WITH-MUTEX : cpu=(sum=29270655 avg= 975688) real= 1725458
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GRAB+RELEASE : cpu=(sum=29194555 avg= 973151) real= 1616391
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ALGO2 : cpu=(sum=25331922 avg= 844397) real= 1331460 [2911750 calls]
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ALGO2+ : cpu=(sum=25128049 avg= 837601) real= 1291458 [1111621 calls]
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ALGO3 : cpu=(sum=25039192 avg= 834639) real= 1310660 [2912492 calls]
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ALGO3+ : cpu=(sum=24520302 avg= 817343) real= 1261327 [1069574 calls]
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* (sb-thread::test-n-threads 35)
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WITH-MUTEX : cpu=(sum=35886189 avg= 1025319) real= 1958961
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GRAB+RELEASE : cpu=(sum=32335690 avg= 923876) real= 1894504
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ALGO2 : cpu=(sum=29280055 avg= 836573) real= 1557933 [3395447 calls]
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ALGO2+ : cpu=(sum=28854572 avg= 824416) real= 1490965 [1276195 calls]
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ALGO3 : cpu=(sum=28764304 avg= 821837) real= 1539534 [3389637 calls]
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ALGO3+ : cpu=(sum=27708686 avg= 791676) real= 1467193 [1239603 calls]
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* (sb-thread::test-n-threads 40)
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WITH-MUTEX : cpu=(sum=40892193 avg= 1022304) real= 2209987
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GRAB+RELEASE : cpu=(sum=37467476 avg= 936686) real= 2130089
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ALGO2 : cpu=(sum=34310107 avg= 857752) real= 1765091 [3882825 calls]
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ALGO2+ : cpu=(sum=33543491 avg= 838587) real= 1711993 [1455625 calls]
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ALGO3 : cpu=(sum=32834489 avg= 820862) real= 1724991 [3878370 calls]
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ALGO3+ : cpu=(sum=29716033 avg= 742900) real= 1669290 [1378376 calls]
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* (sb-thread::test-n-threads 45)
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WITH-MUTEX : cpu=(sum=47760154 avg= 1061336) real= 2463454
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GRAB+RELEASE : cpu=(sum=45402624 avg= 1008947) real= 2385232
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ALGO2 : cpu=(sum=36951436 avg= 821143) real= 1971723 [4363504 calls]
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ALGO2+ : cpu=(sum=36382508 avg= 808500) real= 1918567 [1626474 calls]
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ALGO3 : cpu=(sum=37765508 avg= 839233) real= 1934301 [4365986 calls]
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ALGO3+ : cpu=(sum=37104282 avg= 824539) real= 1842213 [1582110 calls]
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* (sb-thread::test-n-threads 50)
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WITH-MUTEX : cpu=(sum=51003010 avg= 1020060) real= 2775826
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GRAB+RELEASE : cpu=(sum=50266070 avg= 1005321) real= 2643187
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ALGO2 : cpu=(sum=42814331 avg= 856286) real= 2179588 [4851758 calls]
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ALGO2+ : cpu=(sum=40166972 avg= 803339) real= 2121509 [1795256 calls]
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ALGO3 : cpu=(sum=40122437 avg= 802448) real= 2167029 [4843515 calls]
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ALGO3+ : cpu=(sum=40284932 avg= 805698) real= 2058550 [1743178 calls]
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* (sb-thread::test-n-threads 55)
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WITH-MUTEX : cpu=(sum=55076760 avg= 1001395) real= 3008711
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GRAB+RELEASE : cpu=(sum=56878995 avg= 1034163) real= 2877731
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ALGO2 : cpu=(sum=46343366 avg= 842606) real= 2402168 [5331893 calls]
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ALGO2+ : cpu=(sum=43091002 avg= 783472) real= 2330753 [1938588 calls]
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ALGO3 : cpu=(sum=45509126 avg= 827438) real= 2342314 [5345695 calls]
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ALGO3+ : cpu=(sum=45191331 avg= 821660) real= 2260789 [1909666 calls]
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|#
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@ -732,6 +732,81 @@ returns NIL each time."
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(declare (dynamic-extent #'cas))
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(%%wait-for #'cas stop-sec stop-usec)))))
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#+mutex-benchmarks
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(symbol-macrolet ((val (mutex-state mutex)))
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(export '(wait-for-mutex-algorithm-2
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wait-for-mutex-algorithm-3
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wait-for-mutex-2-partial-inline
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wait-for-mutex-3-partial-inline))
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(declaim (sb-ext:maybe-inline %wait-for-mutex-algorithm-2
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%wait-for-mutex-algorithm-3))
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(sb-ext:define-load-time-global *grab-mutex-calls-performed* 0)
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;; Like futex-wait but without garbage having to do with re-invoking
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;; a wake on account of async unwind while releasing the mutex.
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(declaim (inline fast-futex-wait))
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(defun fast-futex-wait (word-addr oldval to-sec to-usec)
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(with-alien ((%wait (function int unsigned
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#+freebsd unsigned #-freebsd (unsigned 32)
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long unsigned-long)
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:extern "futex_wait"))
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(alien-funcall %wait word-addr oldval to-sec to-usec)))
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(defun %wait-for-mutex-algorithm-2 (mutex)
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(incf *grab-mutex-calls-performed*)
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(let* ((mutex (sb-ext:truly-the mutex mutex))
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(c (sb-ext:cas val 0 1))) ; available -> taken
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(unless (= c 0) ; Got it right off the bat?
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(loop
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;; Mark it as contested, and sleep, unless it is now in state 0.
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(when (or (eql c 2) (/= 0 (sb-ext:cas val 1 2)))
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(with-pinned-objects (mutex)
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(fast-futex-wait (mutex-state-address mutex) 2 -1 0)))
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;; Try to get it, still marking it as contested.
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(when (= 0 (setq c (sb-ext:cas val 0 2))) (return)))))) ; win
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(defun %wait-for-mutex-algorithm-3 (mutex)
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(incf *grab-mutex-calls-performed*)
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(let* ((mutex (sb-ext:truly-the mutex mutex))
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(c (sb-ext:cas val 0 1))) ; available -> taken
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(unless (= c 0) ; Got it right off the bat?
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(unless (= c 2)
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(setq c (%raw-instance-xchg/word mutex (get-dsd-index mutex state) 2)))
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(loop while (/= c 0)
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do (with-pinned-objects (mutex)
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(fast-futex-wait (mutex-state-address mutex) 2 -1 0))
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(setq c (%raw-instance-xchg/word mutex (get-dsd-index mutex state) 2))))))
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(defun wait-for-mutex-algorithm-2 (mutex)
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(declare (inline %wait-for-mutex-algorithm-2))
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(let ((mutex (sb-ext:truly-the mutex mutex)))
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(%wait-for-mutex-algorithm-2 mutex)
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(setf (mutex-%owner mutex) *current-thread*)))
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;; The improvement with algorithm 3 is fairly negligible.
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;; Code size is a little less. More improvement comes from doing the
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;; partial-inline algorithms which perform one CAS without a function call.
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(defun wait-for-mutex-algorithm-3 (mutex)
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(declare (inline %wait-for-mutex-algorithm-3))
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(let ((mutex (sb-ext:truly-the mutex mutex)))
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(%wait-for-mutex-algorithm-3 mutex)
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(setf (mutex-%owner mutex) *current-thread*)))
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(defmacro wait-for-mutex-2-partial-inline (mutex)
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`(let ((m ,mutex))
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(or (= (sb-ext:cas (mutex-state m) 0 1) 0) (%wait-for-mutex-algorithm-2 m))
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(setf (mutex-%owner m) *current-thread*)))
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(defmacro wait-for-mutex-3-partial-inline (mutex)
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`(let ((m ,mutex))
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(or (= (sb-ext:cas (mutex-state m) 0 1) 0) (%wait-for-mutex-algorithm-3 m))
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(setf (mutex-%owner m) *current-thread*)))
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;; This is like RELEASE-MUTEX but without keyword arg parsing
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;; and all the different error modes.
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(export 'fast-release-mutex)
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(defun fast-release-mutex (mutex)
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(let ((mutex (sb-ext:truly-the mutex mutex)))
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(setf (mutex-%owner mutex) nil)
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(unless (eql (sb-ext:atomic-decf (mutex-state mutex) 1) 1)
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(setf (mutex-state mutex) 0)
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(with-pinned-objects (mutex)
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(futex-wake (mutex-state-address mutex) 1))))))
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#+sb-thread
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(defun %wait-for-mutex (mutex self timeout to-sec to-usec stop-sec stop-usec deadlinep)
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(declare (sb-ext:muffle-conditions sb-ext:compiler-note))
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@ -1659,7 +1659,7 @@ is a good idea, but see SB-SYS re. blurring of boundaries."
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"%VECTOR-RAW-BITS"
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"%SCALB" "%SCALBN"
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"%RAW-INSTANCE-ATOMIC-INCF/WORD"
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"%RAW-INSTANCE-CAS/WORD"
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"%RAW-INSTANCE-CAS/WORD" "%RAW-INSTANCE-XCHG/WORD"
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"%RAW-INSTANCE-REF/WORD" "%RAW-INSTANCE-SET/WORD"
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"%RAW-INSTANCE-CAS/SIGNED-WORD"
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"%RAW-INSTANCE-REF/SIGNED-WORD" "%RAW-INSTANCE-SET/SIGNED-WORD"
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@ -2934,6 +2934,8 @@ no guarantees of interface stability."
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"W_OK" "X_OK"
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"SC-NPROCESSORS-ONLN"
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"VOID-SYSCALL"
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"CLOCK-THREAD-CPUTIME-ID"
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"CLOCK-PROCESS-CPUTIME-ID"
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;; signals
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"SIGALRM" "SIGBUS" "SIGCHLD" "SIGCONT" "SIGEMT" "SIGFPE"
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@ -231,6 +231,7 @@
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#+riscv
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(defknown %raw-instance-cas/signed-word (instance index sb-vm:signed-word sb-vm:signed-word)
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sb-vm:signed-word ())
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(defknown %raw-instance-xchg/word (instance index sb-vm:word) sb-vm:word ())
|
||||
|
||||
#.`(progn
|
||||
,@(map 'list
|
||||
|
|
|
|||
|
|
@ -767,6 +767,27 @@
|
|||
(define-full-compare-and-swap %raw-instance-cas/word instance
|
||||
instance-slots-offset instance-pointer-lowtag
|
||||
(unsigned-reg) unsigned-num %raw-instance-cas/word)
|
||||
(define-vop ()
|
||||
(:translate %raw-instance-xchg/word)
|
||||
(:policy :fast-safe)
|
||||
(:args (instance :scs (descriptor-reg))
|
||||
(newval :scs (unsigned-reg immediate constant) :target result))
|
||||
(:info index)
|
||||
(:arg-types * (:constant integer) unsigned-num)
|
||||
(:results (result :scs (unsigned-reg)))
|
||||
(:result-types unsigned-num)
|
||||
(:generator 3
|
||||
;; Use RESULT as the source of the exchange, unless doing so
|
||||
;; would clobber NEWVAL
|
||||
(let ((source (if (location= result instance) temp-reg-tn result)))
|
||||
(if (sc-is newval immediate)
|
||||
(inst mov source (constantize (tn-value newval)))
|
||||
(move source newval))
|
||||
(inst xchg (ea (- (ash (+ instance-slots-offset index) word-shift)
|
||||
instance-pointer-lowtag) instance)
|
||||
source)
|
||||
(unless (eq source result)
|
||||
(move result temp-reg-tn)))))
|
||||
|
||||
;;;; code object frobbing
|
||||
|
||||
|
|
|
|||
Loading…
Reference in a new issue