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authorTavian Barnes <tavianator@tavianator.com>2023-11-01 11:18:39 -0400
committerTavian Barnes <tavianator@tavianator.com>2023-11-01 11:26:37 -0400
commitb2ab7a151fca517f4879e76e626ec85ad3de97c7 (patch)
treef4d7a7677c1def09332e3e3a1f5c4ce53486c6f2 /src
parent8aaf670c13ade259f7bcdd50332968c1c6290b34 (diff)
downloadbfs-b2ab7a151fca517f4879e76e626ec85ad3de97c7.tar.xz
bftw: Improve ioq balancing logic
Diffstat (limited to 'src')
-rw-r--r--src/bftw.c35
1 files changed, 22 insertions, 13 deletions
diff --git a/src/bftw.c b/src/bftw.c
index 3982515..5a55037 100644
--- a/src/bftw.c
+++ b/src/bftw.c
@@ -430,6 +430,8 @@ struct bftw_state {
struct ioq *ioq;
/** The number of I/O threads. */
size_t nthreads;
+ /** Tracks the imbalance between main thread and background I/O. */
+ long imbalance;
/** A batch of directories to open. */
struct bftw_list dir_batch;
@@ -541,6 +543,8 @@ static int bftw_state_init(struct bftw_state *state, const struct bftw_args *arg
state->dir_flags |= BFS_DIR_WHITEOUTS;
}
+ state->imbalance = 0;
+
SLIST_INIT(&state->dir_batch);
SLIST_INIT(&state->to_open);
SLIST_INIT(&state->to_read);
@@ -571,6 +575,12 @@ static void bftw_unpin_dir(struct bftw_state *state, struct bftw_file *file, boo
}
}
+/** Adjust the I/O queue balance. */
+static void bftw_ioq_balance(struct bftw_state *state, long delta) {
+ // Avoid signed overflow
+ state->imbalance = (unsigned long)state->imbalance + (unsigned long)delta;
+}
+
/** Pop a response from the I/O queue. */
static int bftw_ioq_pop(struct bftw_state *state, bool block) {
struct ioq *ioq = state->ioq;
@@ -627,13 +637,6 @@ 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;
@@ -641,11 +644,19 @@ static int bftw_ioq_reserve(struct bftw_state *state) {
return -1;
}
+ // With only one background thread, we should balance I/O between it and
+ // the main thread. With more than one background thread, it's faster
+ // to wait on background I/O than it is to do it on the main thread.
+ bool balance = state->nthreads <= 1;
+ if (balance && state->imbalance < 0) {
+ return -1;
+ }
+
if (ioq_capacity(ioq) > 0) {
return 0;
}
- if (bftw_ioq_pop(state, bftw_ioq_block(state)) < 0) {
+ if (bftw_ioq_pop(state, !balance) < 0) {
return -1;
}
@@ -880,6 +891,7 @@ static int bftw_ioq_opendir(struct bftw_state *state, struct bftw_file *file) {
file->ioqueued = true;
--cache->capacity;
+ bftw_ioq_balance(state, -1);
return 0;
free:
@@ -899,11 +911,6 @@ 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;
- }
}
}
@@ -1041,6 +1048,8 @@ static struct bfs_dir *bftw_file_opendir(struct bftw_state *state, struct bftw_f
return NULL;
}
+ bftw_ioq_balance(state, +1);
+
if (bfs_opendir(dir, fd, NULL, state->dir_flags) != 0) {
bftw_freedir(cache, dir);
return NULL;