bftw: Leave work for the main thread if profitable

diff --git a/src/bftw.c b/src/bftw.c
index dff949f0d977cb5c35eb54500207cec478da11ce..398251558df73d0cddc82441a2ae49906a83efc8 100644 (file)
--- a/src/bftw.c
+++ b/src/bftw.c
@@ -627,6 +627,13 @@ static int bftw_ioq_pop(struct bftw_state *state, bool block) {
        return op;
 }
 
+/** Check if we should block on the I/O queue even if not strictly necessary. */
+static bool bftw_ioq_block(const struct bftw_state *state) {
+       // With more than two threads, it is faster to wait for an I/O
+       // operation to complete than it is to do it ourselves
+       return state->nthreads > 2;
+}
+
 /** Try to reserve space in the I/O queue. */
 static int bftw_ioq_reserve(struct bftw_state *state) {
        struct ioq *ioq = state->ioq;
@@ -638,10 +645,7 @@ static int bftw_ioq_reserve(struct bftw_state *state) {
                return 0;
        }
 
-       // With more than two threads, it is faster to wait for an I/O operation
-       // to complete than it is to do it ourselves
-       bool block = state->nthreads > 2;
-       if (bftw_ioq_pop(state, block) < 0) {
+       if (bftw_ioq_pop(state, bftw_ioq_block(state)) < 0) {
                return -1;
        }
 
@@ -895,6 +899,11 @@ static void bftw_ioq_opendirs(struct bftw_state *state, struct bftw_list *queue)
                        break;
                }
                SLIST_POP(queue);
+
+               if (!bftw_ioq_block(state)) {
+                       // Leave some work for the main thread
+                       break;
+               }
        }
 }