From: Alexey Dobriyan <adobriyan@gmail.com>
To: kbusch@kernel.org, axboe@fb.com, hch@lst.de, sagi@grimberg.me
Cc: linux-nvme@lists.infradead.org
Subject: [PATCH] nvme-pci: slimmer CQ head update
Date: Fri, 28 Feb 2020 21:45:19 +0300 [thread overview]
Message-ID: <20200228184519.GA2281@avx2> (raw)
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>
---
drivers/nvme/host/pci.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
--- 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;
}
}
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next reply other threads:[~2020-02-28 18:45 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-28 18:45 Alexey Dobriyan [this message]
2020-02-29 5:53 ` [PATCH] nvme-pci: slimmer CQ head update Keith Busch
2020-05-06 11:03 ` John Garry
2020-05-06 12:47 ` Keith Busch
2020-05-06 13:24 ` Alexey Dobriyan
2020-05-06 13:44 ` John Garry
2020-05-06 14:01 ` Alexey Dobriyan
2020-05-06 14:35 ` Christoph Hellwig
2020-05-06 16:26 ` John Garry
2020-05-06 16:31 ` Will Deacon
2020-05-06 16:52 ` Robin Murphy
2020-05-06 17:02 ` John Garry
2020-05-07 8:18 ` John Garry
2020-05-07 11:04 ` Robin Murphy
2020-05-07 13:55 ` John Garry
2020-05-07 14:23 ` Keith Busch
2020-05-07 15:11 ` John Garry
2020-05-07 15:35 ` Keith Busch
2020-05-07 15:41 ` John Garry
2020-05-08 16:16 ` Keith Busch
2020-05-08 17:04 ` John Garry
2020-05-07 16:26 ` Robin Murphy
2020-05-07 17:35 ` Keith Busch
2020-05-07 17:44 ` Will Deacon
2020-05-07 18:06 ` Keith Busch
2020-05-08 11:40 ` Will Deacon
2020-05-08 14:07 ` Keith Busch
2020-05-08 15:34 ` Keith Busch
2020-05-06 14:44 ` Keith Busch
2020-05-07 15:58 ` Keith Busch
2020-05-07 20:07 ` [PATCH] nvme-pci: fix "slimmer CQ head update" Alexey Dobriyan
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