Switch blas_server to use acq/rel semantics
Heavy-weight locking isn't required to pass the work queue pointer between threads and simple atomic acquire/release semantics can be used instead. This is especially important as pthread_mutex_lock() isn't fair. We've observed substantial variation in runtime because of the the unfairness of these locks which complety goes away with this implementation. The locks themselves are left to provide a portable way for idling threads to sleep/wakeup after many unsuccessful iterations waiting.
This commit is contained in:
Ali Saidi
parent
430ee31e66
commit
43c2e845ab
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@ -140,6 +140,16 @@ typedef struct {
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} thread_status_t;
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#if (__STDC_VERSION__ >= 201112L)
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#define atomic_load_queue(p) __atomic_load_n(p, __ATOMIC_RELAXED)
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#define atomic_store_queue(p, v) __atomic_store_n(p, v, __ATOMIC_RELAXED)
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#else
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#define atomic_load_queue(p) (blas_queue_t*)(*(volatile blas_queue_t**)(p))
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#define atomic_store_queue(p, v) (*(volatile blas_queue_t* volatile*)(p) = (v))
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#endif
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static thread_status_t thread_status[MAX_CPU_NUMBER] __attribute__((aligned(ATTRIBUTE_SIZE)));
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#ifndef THREAD_TIMEOUT
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@ -312,20 +322,19 @@ blas_queue_t *tscq;
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last_tick = (unsigned int)rpcc();
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pthread_mutex_lock (&thread_status[cpu].lock);
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tscq=thread_status[cpu].queue;
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pthread_mutex_unlock (&thread_status[cpu].lock);
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tscq = atomic_load_queue(&thread_status[cpu].queue);
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while(!tscq) {
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YIELDING;
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if ((unsigned int)rpcc() - last_tick > thread_timeout) {
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pthread_mutex_lock (&thread_status[cpu].lock);
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if (!thread_status[cpu].queue) {
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if (!atomic_load_queue(&thread_status[cpu].queue)) {
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pthread_mutex_lock (&thread_status[cpu].lock);
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thread_status[cpu].status = THREAD_STATUS_SLEEP;
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while (thread_status[cpu].status == THREAD_STATUS_SLEEP) {
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while (thread_status[cpu].status == THREAD_STATUS_SLEEP &&
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!atomic_load_queue(&thread_status[cpu].queue)) {
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#ifdef MONITOR
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main_status[cpu] = MAIN_SLEEPING;
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@ -333,19 +342,18 @@ blas_queue_t *tscq;
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pthread_cond_wait(&thread_status[cpu].wakeup, &thread_status[cpu].lock);
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}
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pthread_mutex_unlock(&thread_status[cpu].lock);
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}
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pthread_mutex_unlock(&thread_status[cpu].lock);
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last_tick = (unsigned int)rpcc();
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}
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pthread_mutex_lock (&thread_status[cpu].lock);
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tscq=thread_status[cpu].queue;
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pthread_mutex_unlock (&thread_status[cpu].lock);
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tscq = atomic_load_queue(&thread_status[cpu].queue);
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}
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queue = thread_status[cpu].queue;
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queue = atomic_load_queue(&thread_status[cpu].queue);
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MB;
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if ((long)queue == -1) break;
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@ -360,9 +368,7 @@ blas_queue_t *tscq;
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if (queue) {
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int (*routine)(blas_arg_t *, void *, void *, void *, void *, BLASLONG) = queue -> routine;
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pthread_mutex_lock (&thread_status[cpu].lock);
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thread_status[cpu].queue = (blas_queue_t *)1;
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pthread_mutex_unlock (&thread_status[cpu].lock);
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atomic_store_queue(&thread_status[cpu].queue, (blas_queue_t *)1);
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sa = queue -> sa;
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sb = queue -> sb;
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@ -442,13 +448,9 @@ blas_queue_t *tscq;
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// arm: make sure all results are written out _before_
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// thread is marked as done and other threads use them
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WMB;
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MB;
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atomic_store_queue(&thread_status[cpu].queue, (blas_queue_t *)0);
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pthread_mutex_lock (&thread_status[cpu].lock);
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thread_status[cpu].queue = (blas_queue_t * volatile) ((long)thread_status[cpu].queue & 0); /* Need a trick */
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pthread_mutex_unlock (&thread_status[cpu].lock);
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WMB;
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}
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@ -566,12 +568,9 @@ int blas_thread_init(void){
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for(i = 0; i < blas_num_threads - 1; i++){
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thread_status[i].queue = (blas_queue_t *)NULL;
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atomic_store_queue(&thread_status[i].queue, (blas_queue_t *)0);
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thread_status[i].status = THREAD_STATUS_WAKEUP;
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pthread_mutex_init(&thread_status[i].lock, NULL);
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pthread_cond_init (&thread_status[i].wakeup, NULL);
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#ifdef NEED_STACKATTR
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ret=pthread_create(&blas_threads[i], &attr,
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&blas_thread_server, (void *)i);
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@ -655,7 +654,8 @@ int exec_blas_async(BLASLONG pos, blas_queue_t *queue){
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if (queue -> mode & BLAS_NODE) {
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do {
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while((thread_status[i].node != node || thread_status[i].queue) && (i < blas_num_threads - 1)) i ++;
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while((thread_status[i].node != node || atomic_load_queue(&thread_status[i].queue)) && (i < blas_num_threads - 1)) i ++;
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if (i < blas_num_threads - 1) break;
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@ -669,36 +669,26 @@ int exec_blas_async(BLASLONG pos, blas_queue_t *queue){
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} while (1);
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} else {
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pthread_mutex_lock (&thread_status[i].lock);
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tsiq = thread_status[i].queue;
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pthread_mutex_unlock (&thread_status[i].lock);
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tsiq = atomic_load_queue(&thread_status[i].queue);
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while(tsiq) {
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i ++;
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if (i >= blas_num_threads - 1) i = 0;
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pthread_mutex_lock (&thread_status[i].lock);
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tsiq = thread_status[i].queue;
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pthread_mutex_unlock (&thread_status[i].lock);
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tsiq = atomic_load_queue(&thread_status[i].queue);
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}
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}
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#else
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pthread_mutex_lock (&thread_status[i].lock);
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tsiq=thread_status[i].queue ;
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pthread_mutex_unlock (&thread_status[i].lock);
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tsiq = atomic_load_queue(&thread_status[i].queue);
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while(tsiq) {
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i ++;
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if (i >= blas_num_threads - 1) i = 0;
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pthread_mutex_lock (&thread_status[i].lock);
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tsiq=thread_status[i].queue ;
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pthread_mutex_unlock (&thread_status[i].lock);
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tsiq = atomic_load_queue(&thread_status[i].queue);
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}
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#endif
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queue -> assigned = i;
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WMB;
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pthread_mutex_lock (&thread_status[i].lock);
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thread_status[i].queue = queue;
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pthread_mutex_unlock (&thread_status[i].lock);
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WMB;
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MB;
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atomic_store_queue(&thread_status[i].queue, queue);
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queue = queue -> next;
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pos ++;
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@ -718,9 +708,7 @@ int exec_blas_async(BLASLONG pos, blas_queue_t *queue){
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pos = current -> assigned;
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pthread_mutex_lock (&thread_status[pos].lock);
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tspq=thread_status[pos].queue;
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pthread_mutex_unlock (&thread_status[pos].lock);
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tspq = atomic_load_queue(&thread_status[pos].queue);
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if ((BLASULONG)tspq > 1) {
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pthread_mutex_lock (&thread_status[pos].lock);
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@ -752,24 +740,20 @@ int exec_blas_async_wait(BLASLONG num, blas_queue_t *queue){
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while ((num > 0) && queue) {
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pthread_mutex_lock(&thread_status[queue->assigned].lock);
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tsqq=thread_status[queue -> assigned].queue;
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pthread_mutex_unlock(&thread_status[queue->assigned].lock);
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tsqq = atomic_load_queue(&thread_status[queue->assigned].queue);
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while(tsqq) {
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YIELDING;
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pthread_mutex_lock(&thread_status[queue->assigned].lock);
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tsqq=thread_status[queue -> assigned].queue;
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pthread_mutex_unlock(&thread_status[queue->assigned].lock);
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tsqq = atomic_load_queue(&thread_status[queue->assigned].queue);
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};
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queue = queue -> next;
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num --;
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}
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MB;
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#ifdef SMP_DEBUG
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fprintf(STDERR, "Done.\n\n");
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#endif
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@ -880,7 +864,7 @@ void goto_set_num_threads(int num_threads) {
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for(i = blas_num_threads - 1; i < num_threads - 1; i++){
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thread_status[i].queue = (blas_queue_t *)NULL;
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atomic_store_queue(&thread_status[i].queue, (blas_queue_t *)0);
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thread_status[i].status = THREAD_STATUS_WAKEUP;
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pthread_mutex_init(&thread_status[i].lock, NULL);
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@ -971,12 +955,11 @@ int BLASFUNC(blas_thread_shutdown)(void){
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for (i = 0; i < blas_num_threads - 1; i++) {
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pthread_mutex_lock (&thread_status[i].lock);
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thread_status[i].queue = (blas_queue_t *)-1;
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atomic_store_queue(&thread_status[i].queue, (blas_queue_t *)-1);
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thread_status[i].status = THREAD_STATUS_WAKEUP;
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pthread_cond_signal (&thread_status[i].wakeup);
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pthread_mutex_unlock(&thread_status[i].lock);
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