nvme-pci: remove volatile cqes

The completion queue entry is not volatile once the phase is confirmed.
Remove the volatile keywords and check the phase using the appropriate
READ_ONCE() accessor, allowing the compiler to optimize the remaining
completion path.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index e13c370..e95c746 100644 (file)
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -166,7 +166,7 @@ struct nvme_queue {
        void *sq_cmds;
         /* only used for poll queues: */
        spinlock_t cq_poll_lock ____cacheline_aligned_in_smp;
-       volatile struct nvme_completion *cqes;
+       struct nvme_completion *cqes;
        dma_addr_t sq_dma_addr;
        dma_addr_t cq_dma_addr;
        u32 __iomem *q_db;
@@ -922,8 +922,9 @@ static void nvme_pci_complete_rq(struct request *req)
 /* We read the CQE phase first to check if the rest of the entry is valid */
 static inline bool nvme_cqe_pending(struct nvme_queue *nvmeq)
 {
-       return (le16_to_cpu(nvmeq->cqes[nvmeq->cq_head].status) & 1) ==
-                       nvmeq->cq_phase;
+       struct nvme_completion *hcqe = &nvmeq->cqes[nvmeq->cq_head];
+
+       return (le16_to_cpu(READ_ONCE(hcqe->status)) & 1) == nvmeq->cq_phase;
 }
 
 static inline void nvme_ring_cq_doorbell(struct nvme_queue *nvmeq)
@@ -944,7 +945,7 @@ static inline struct blk_mq_tags *nvme_queue_tagset(struct nvme_queue *nvmeq)
 
 static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx)
 {
-       volatile struct nvme_completion *cqe = &nvmeq->cqes[idx];
+       struct nvme_completion *cqe = &nvmeq->cqes[idx];
        struct request *req;
 
        if (unlikely(cqe->command_id >= nvmeq->q_depth)) {