121 lines · cpp
1// Mini-benchmark for tsan VTS worst case performance2// Idea:3// 1) Spawn M + N threads (M >> N)4// We'll call the 'M' threads as 'garbage threads'.5// 2) Make sure all threads have created thus no TIDs were reused6// 3) Join the garbage threads7// 4) Do many sync operations on the remaining N threads8//9// It turns out that due to O(M+N) VTS complexity the (4) is much slower with10// when N is large.11//12// Some numbers:13// a) clang++ native O1 with n_iterations=200kk takes14// 5s regardless of M15// clang++ tsanv2 O1 with n_iterations=20kk takes16// 23.5s with M=20017// 11.5s with M=118// i.e. tsanv2 is ~23x to ~47x slower than native, depends on M.19// b) g++ native O1 with n_iterations=200kk takes20// 5.5s regardless of M21// g++ tsanv1 O1 with n_iterations=2kk takes22// 39.5s with M=20023// 20.5s with M=124// i.e. tsanv1 is ~370x to ~720x slower than native, depends on M.25 26#include <assert.h>27#include <pthread.h>28#include <stdio.h>29#include <stdlib.h>30 31class __attribute__((aligned(64))) Mutex {32 public:33 Mutex() { pthread_mutex_init(&m_, NULL); }34 ~Mutex() { pthread_mutex_destroy(&m_); }35 void Lock() { pthread_mutex_lock(&m_); }36 void Unlock() { pthread_mutex_unlock(&m_); }37 38 private:39 pthread_mutex_t m_;40};41 42const int kNumMutexes = 1024;43Mutex mutexes[kNumMutexes];44 45int n_threads, n_iterations;46 47pthread_barrier_t all_threads_ready, main_threads_ready;48 49void* GarbageThread(void *unused) {50 pthread_barrier_wait(&all_threads_ready);51 return 0;52}53 54void *Thread(void *arg) {55 long idx = (long)arg;56 pthread_barrier_wait(&all_threads_ready);57 58 // Wait for the main thread to join the garbage threads.59 pthread_barrier_wait(&main_threads_ready);60 61 printf("Thread %ld go!\n", idx);62 int offset = idx * kNumMutexes / n_threads;63 for (int i = 0; i < n_iterations; i++) {64 mutexes[(offset + i) % kNumMutexes].Lock();65 mutexes[(offset + i) % kNumMutexes].Unlock();66 }67 printf("Thread %ld done\n", idx);68 return 0;69}70 71int main(int argc, char **argv) {72 int n_garbage_threads;73 if (argc == 1) {74 n_threads = 2;75 n_garbage_threads = 200;76 n_iterations = 20000000;77 } else if (argc == 4) {78 n_threads = atoi(argv[1]);79 assert(n_threads > 0 && n_threads <= 32);80 n_garbage_threads = atoi(argv[2]);81 assert(n_garbage_threads > 0 && n_garbage_threads <= 16000);82 n_iterations = atoi(argv[3]);83 } else {84 printf("Usage: %s n_threads n_garbage_threads n_iterations\n", argv[0]);85 return 1;86 }87 printf("%s: n_threads=%d n_garbage_threads=%d n_iterations=%d\n",88 __FILE__, n_threads, n_garbage_threads, n_iterations);89 90 pthread_barrier_init(&all_threads_ready, NULL, n_garbage_threads + n_threads + 1);91 pthread_barrier_init(&main_threads_ready, NULL, n_threads + 1);92 93 pthread_t *t = new pthread_t[n_threads];94 {95 pthread_t *g_t = new pthread_t[n_garbage_threads];96 for (int i = 0; i < n_garbage_threads; i++) {97 int status = pthread_create(&g_t[i], 0, GarbageThread, NULL);98 assert(status == 0);99 }100 for (int i = 0; i < n_threads; i++) {101 int status = pthread_create(&t[i], 0, Thread, (void*)i);102 assert(status == 0);103 }104 pthread_barrier_wait(&all_threads_ready);105 printf("All threads started! Killing the garbage threads.\n");106 for (int i = 0; i < n_garbage_threads; i++) {107 pthread_join(g_t[i], 0);108 }109 delete [] g_t;110 }111 printf("Resuming the main threads.\n");112 pthread_barrier_wait(&main_threads_ready);113 114 115 for (int i = 0; i < n_threads; i++) {116 pthread_join(t[i], 0);117 }118 delete [] t;119 return 0;120}121