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93 lines
2.3 KiB
C
93 lines
2.3 KiB
C
/* How expensive is
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* - Obtaining a read-only lock for the first obtainer.
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* - Obtaining it for the second one?
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* - The third one? */
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#include <assert.h>
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#include <pthread.h>
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#include <stdio.h>
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#include <sys/time.h>
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float tdiff (struct timeval *start, struct timeval *end) {
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return 1e6*(end->tv_sec-start->tv_sec) +(end->tv_usec - start->tv_usec);
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}
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/* My own rwlock implementation. */
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struct brwl {
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int mutex;
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int state; // 0 for unlocked, -1 for a writer, otherwise many readers
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};
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static inline int xchg(volatile int *ptr, int x)
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{
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__asm__("xchgl %0,%1" :"=r" (x) :"m" (*(ptr)), "0" (x) :"memory");
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return x;
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}
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static inline void sfence (void) {
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asm volatile ("sfence":::"memory");
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}
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static inline void brwl_rlock (struct brwl *l) {
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while (xchg(&l->mutex, 1)) ;
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l->state++;
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#if 1
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sfence();
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l->mutex=0;
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#else
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xchg(&l->mutex, 0);
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#endif
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}
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enum {K=1000};
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pthread_rwlock_t rwlocks[K];
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struct brwl blocks[K];
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int main (int argc __attribute__((__unused__)), char *argv[] __attribute__((__unused__))) {
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int j;
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int i;
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int r;
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struct timeval start, end;
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for (j=0; j<3; j++) {
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for (i=0; i<K; i++) {
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r=pthread_rwlock_init(&rwlocks[i], NULL);
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assert(r==0);
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}
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gettimeofday(&start, 0);
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for (i=0; i<K; i++) {
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r = pthread_rwlock_tryrdlock(&rwlocks[i]);
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assert(r==0);
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}
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gettimeofday(&end, 0);
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printf("pthread_rwlock_tryrdlock took %9.3fus for %d ops: %9.3fus/lock (%9.3fMops/s)\n", tdiff(&start,&end), K, tdiff(&start,&end)/K, K/tdiff(&start,&end));
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}
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for (j=0; j<3; j++) {
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for (i=0; i<K; i++) {
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r=pthread_rwlock_init(&rwlocks[i], NULL);
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assert(r==0);
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}
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gettimeofday(&start, 0);
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for (i=0; i<K; i++) {
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r = pthread_rwlock_rdlock(&rwlocks[i]);
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assert(r==0);
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}
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gettimeofday(&end, 0);
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printf("pthread_rwlock_rdlock took %9.3fus for %d ops: %9.3fus/lock (%9.3fMops/s)\n", tdiff(&start,&end), K, tdiff(&start,&end)/K, K/tdiff(&start,&end));
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}
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for (j=0; j<3; j++) {
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for (i=0; i<K; i++) {
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blocks[i].state=0;
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blocks[i].mutex=0;
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}
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gettimeofday(&start, 0);
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for (i=0; i<K; i++) {
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brwl_rlock(&blocks[i]);
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}
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gettimeofday(&end, 0);
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printf("brwl_rlock took %9.3fus for %d ops: %9.3fus/lock (%9.3fMops/s)\n", tdiff(&start,&end), K, tdiff(&start,&end)/K, K/tdiff(&start,&end));
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}
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return 0;
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}
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