Minor improvements for parallel block processor

 - Fewer lock aquires in worker function
   - There is no point in locking/unlocking for inserting the completed
     block if we are going to lock again immediately in the next iteration
   -> Merge those two critical sections into one
 - Constant time queue insertion
 - Bypass queue entirely if there is nothing to do for a block

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 26 insertions, 16 deletions

diff --git a/lib/comp/block_processor_parallel.c b/lib/comp/block_processor_parallel.c
index 617900f..985c900 100644
--- a/lib/comp/block_processor_parallel.c
+++ b/lib/comp/block_processor_parallel.c
@@ -30,6 +30,8 @@ struct block_processor_t {
 
 	/* needs rw access by worker and main thread */
 	block_t *queue;
+	block_t *queue_last;
+
 	block_t *done;
 	bool terminate;
 	size_t backlog;
@@ -73,10 +75,16 @@ static void *worker_proc(void *arg)
 {
 	compress_worker_t *worker = arg;
 	block_processor_t *shared = worker->shared;
-	block_t *blk;
+	block_t *blk = NULL;
 
 	for (;;) {
 		pthread_mutex_lock(&shared->mtx);
+		if (blk != NULL) {
+			store_completed_block(shared, blk);
+			shared->backlog -= 1;
+			pthread_cond_broadcast(&shared->done_cond);
+		}
+
 		while (shared->queue == NULL && !shared->terminate) {
 			pthread_cond_wait(&shared->queue_cond,
 					  &shared->mtx);
@@ -90,18 +98,15 @@ static void *worker_proc(void *arg)
 		blk = shared->queue;
 		shared->queue = blk->next;
 		blk->next = NULL;
+
+		if (shared->queue == NULL)
+			shared->queue_last = NULL;
 		pthread_mutex_unlock(&shared->mtx);
 
 		if (process_block(blk, worker->cmp, worker->scratch,
 				  shared->max_block_size)) {
 			blk->flags |= BLK_COMPRESS_ERROR;
 		}
-
-		pthread_mutex_lock(&shared->mtx);
-		store_completed_block(shared, blk);
-		shared->backlog -= 1;
-		pthread_cond_broadcast(&shared->done_cond);
-		pthread_mutex_unlock(&shared->mtx);
 	}
 	return NULL;
 }
@@ -273,18 +278,23 @@ int block_processor_enqueue(block_processor_t *proc, block_t *block)
 	block->next = NULL;
 
 	pthread_mutex_lock(&proc->mtx);
-	while (proc->backlog > proc->num_workers * MAX_BACKLOG_FACTOR)
-		pthread_cond_wait(&proc->done_cond, &proc->mtx);
-
-	if (proc->queue == NULL) {
-		proc->queue = block;
+	if ((block->flags & BLK_DONT_COMPRESS) &&
+	    (block->flags & BLK_DONT_CHECKSUM)) {
+		store_completed_block(proc, block);
 	} else {
-		for (it = proc->queue; it->next != NULL; it = it->next)
-			;
-		it->next = block;
+		while (proc->backlog > proc->num_workers * MAX_BACKLOG_FACTOR)
+			pthread_cond_wait(&proc->done_cond, &proc->mtx);
+
+		if (proc->queue_last == NULL) {
+			proc->queue = proc->queue_last = block;
+		} else {
+			proc->queue_last->next = block;
+			proc->queue_last = block;
+		}
+
+		proc->backlog += 1;
 	}
 
-	proc->backlog += 1;
 	it = proc->done;
 	prev = NULL;