This patch improves the way the RDMA IB signalling is done
by using atomic operations for the signalling variable. This
avoids race conditions on sig_count.
The signalling interval changes slightly and is now the
largest power of two not larger than queue depth / 2.
ilog() usage idea by Bart Van Assche.
Signed-off-by: Marta Rybczynska <marta.rybczyn...@kalray.eu>
Reviewed-by: Sagi Grimberg <s...@grimberg.me>
---
Changes from v1:
* remove nvme_rdma_init_sig_count, put all into
nvme_rdma_queue_sig_limit
---
drivers/nvme/host/rdma.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index 28bd255..4eb4846 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -88,7 +88,7 @@ enum nvme_rdma_queue_flags {
struct nvme_rdma_queue {
struct nvme_rdma_qe *rsp_ring;
- u8 sig_count;
+ atomic_t sig_count;
int queue_size;
size_t cmnd_capsule_len;
struct nvme_rdma_ctrl *ctrl;
@@ -554,6 +554,8 @@ static int nvme_rdma_init_queue(struct nvme_rdma_ctrl *ctrl,
queue->queue_size = queue_size;
+ atomic_set(&queue->sig_count, 0);
+
queue->cm_id = rdma_create_id(&init_net, nvme_rdma_cm_handler, queue,
RDMA_PS_TCP, IB_QPT_RC);
if (IS_ERR(queue->cm_id)) {
@@ -1038,17 +1040,18 @@ static void nvme_rdma_send_done(struct ib_cq *cq,
struct ib_wc *wc)
nvme_rdma_wr_error(cq, wc, "SEND");
}
-static inline int nvme_rdma_queue_sig_limit(struct nvme_rdma_queue *queue)
+static inline bool nvme_rdma_queue_sig_limit(struct nvme_rdma_queue *queue)
{
- int sig_limit;
+ int limit;
- /*
- * We signal completion every queue depth/2 and also handle the
- * degenerated case of a device with queue_depth=1, where we
- * would need to signal every message.
+ /* We want to signal completion at least every queue depth/2.
+ * This returns the largest power of two that is not above half
+ * of (queue size + 1) to optimize (avoid divisions).
*/
- sig_limit = max(queue->queue_size / 2, 1);
- return (++queue->sig_count % sig_limit) == 0;
+ limit = 1 << ilog2((queue->queue_size + 1) / 2);
+
+ /* Signal if sig_count is a multiple of limit */
+ return (atomic_inc_return(&queue->sig_count) & (limit - 1)) == 0;
}
static int nvme_rdma_post_send(struct nvme_rdma_queue *queue,
--
1.8.3.1
