Messages in this thread Patch in this message | | | Date | Mon, 5 Jun 2017 11:45:38 +0200 (CEST) | From | Marta Rybczynska <> | Subject | [PATCH] nvme-rdma: remove race conditions from IB signalling |
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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.rybczynska@kalray.eu> --- drivers/nvme/host/rdma.c | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-)
diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c index 28bd255..80682f7 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 +1040,26 @@ 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 int nvme_rdma_init_sig_count(int queue_size) { - int sig_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; + return 1 << ilog2((queue_size + 1) / 2); +} + +static inline bool nvme_rdma_queue_sig_limit(struct nvme_rdma_queue *queue) +{ + int count, limit; + + limit = nvme_rdma_init_sig_count(queue->queue_size); + count = atomic_inc_return(&queue->sig_count); + + /* Signal if count is a multiple of limit */ + if ((count & (limit - 1)) == 0) + return true; + return false; } static int nvme_rdma_post_send(struct nvme_rdma_queue *queue, -- 1.8.3.1
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