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authorAlexey Dobriyan <adobriyan@gmail.com>2020-02-28 21:45:19 +0300
committerKeith Busch <kbusch@kernel.org>2020-03-26 04:48:06 +0900
commite2a366a4b0feaeba8f0bf6091ddd2ac27507a9d3 (patch)
treef676f87c9dcddaf43314bc84ee3e8fee1120b1a8
parent6d525f9755c2ce444de2f3d604d41fbe4df91a8c (diff)
nvme-pci: slimmer CQ head update
Update CQ head with pre-increment operator. This saves subtraction of 1 and a few registers. Also update phase with "^= 1". This generates only one RMW instruction. ffffffff815ba150 <nvme_update_cq_head>: ffffffff815ba150: 0f b7 47 70 movzx eax,WORD PTR [rdi+0x70] ffffffff815ba154: 83 c0 01 add eax,0x1 ffffffff815ba157: 66 89 47 70 mov WORD PTR [rdi+0x70],ax ffffffff815ba15b: 66 3b 47 68 cmp ax,WORD PTR [rdi+0x68] ffffffff815ba15f: 74 01 je ffffffff815ba162 <nvme_update_cq_head+0x12> ffffffff815ba161: c3 ret ffffffff815ba162: 31 c0 xor eax,eax ffffffff815ba164: 80 77 74 01 ===> xor BYTE PTR [rdi+0x74],0x1 ffffffff815ba168: 66 89 47 70 mov WORD PTR [rdi+0x70],ax ffffffff815ba16c: c3 ret add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-119 (-119) Function old new delta nvme_poll 690 678 -12 nvme_dev_disable 1230 1177 -53 nvme_irq 613 559 -54 Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
-rw-r--r--drivers/nvme/host/pci.c6
1 files changed, 2 insertions, 4 deletions
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index d3f23d6254e4..cdc9b6149d38 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -982,11 +982,9 @@ static void nvme_complete_cqes(struct nvme_queue *nvmeq, u16 start, u16 end)
static inline void nvme_update_cq_head(struct nvme_queue *nvmeq)
{
- if (nvmeq->cq_head == nvmeq->q_depth - 1) {
+ if (++nvmeq->cq_head == nvmeq->q_depth) {
nvmeq->cq_head = 0;
- nvmeq->cq_phase = !nvmeq->cq_phase;
- } else {
- nvmeq->cq_head++;
+ nvmeq->cq_phase ^= 1;
}
}