diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/ioq.c | 25 |
1 files changed, 5 insertions, 20 deletions
@@ -26,15 +26,11 @@ * * Pushes are implemented with an unconditional * - * fetch_add(&ioqq->head, IOQ_STRIDE) + * fetch_add(&ioqq->head, 1) * * which scales better on many architectures than compare-and-swap (see [1] for - * details). Pops are implemented similarly. We add IOQ_STRIDE rather than 1 - * so that successive queue elements are on different cache lines, but the - * exposition below uses 1 for simplicity. - * - * Since the fetch-and-adds are unconditional, non-blocking readers can get - * ahead of writers: + * details). Pops are implemented similarly. Since the fetch-and-adds are + * unconditional, non-blocking readers can get ahead of writers: * * Reader Writer * ──────────────── ────────────────────── @@ -204,17 +200,6 @@ struct ioqq { cache_align ioq_slot slots[]; }; -// If we assign slots sequentially, threads will likely be operating on -// consecutive slots. If these slots are in the same cache line, that will -// result in false sharing. We can mitigate this by assigning slots with a -// stride larger than a cache line e.g. 0, 9, 18, ..., 1, 10, 19, ... -// As long as the stride is relatively prime to circular buffer length, we'll -// still use every available slot. Since the length is a power of two, that -// means the stride must be odd. - -#define IOQ_STRIDE ((FALSE_SHARING_SIZE / sizeof(ioq_slot)) | 1) -bfs_static_assert(IOQ_STRIDE % 2 == 1); - /** Destroy an I/O command queue. */ static void ioqq_destroy(struct ioqq *ioqq) { if (!ioqq) { @@ -357,7 +342,7 @@ static bool ioq_slot_push(struct ioqq *ioqq, ioq_slot *slot, struct ioq_ent *ent /** Push an entry onto the queue. */ static void ioqq_push(struct ioqq *ioqq, struct ioq_ent *ent) { while (true) { - size_t i = fetch_add(&ioqq->head, IOQ_STRIDE, relaxed); + size_t i = fetch_add(&ioqq->head, 1, relaxed); ioq_slot *slot = &ioqq->slots[i & ioqq->slot_mask]; if (ioq_slot_push(ioqq, slot, ent)) { break; @@ -400,7 +385,7 @@ static struct ioq_ent *ioq_slot_pop(struct ioqq *ioqq, ioq_slot *slot, bool bloc /** Pop an entry from the queue. */ static struct ioq_ent *ioqq_pop(struct ioqq *ioqq, bool block) { - size_t i = fetch_add(&ioqq->tail, IOQ_STRIDE, relaxed); + size_t i = fetch_add(&ioqq->tail, 1, relaxed); ioq_slot *slot = &ioqq->slots[i & ioqq->slot_mask]; return ioq_slot_pop(ioqq, slot, block); } |