From: Alexey Dobriyan <adobriyan@gmail.com>
Date: Fri, 28 Feb 2020 21:45:19 +0300
Subject: [PATCH] nvme-pci: slimmer CQ head update
Git-commit: e2a366a4b0feaeba8f0bf6091ddd2ac27507a9d3
Patch-mainline: v5.7-rc1
References: git-fixes
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>
Acked-by: Hannes Reinecke <hare@suse.com>
---
drivers/nvme/host/pci.c | 6 ++----
1 file 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;
}
}
--
2.29.2