2018-01-11 05:12:57

by jianchao.wang

Subject: [PATCH] nvme-pci: calculate iod and avg_seg_size just before use them

The calculation of iod and avg_seg_size maybe meaningless if
nvme_pci_use_sgls returns before uses them. So calculate
just before use them.

Signed-off-by: Jianchao Wang <[email protected]>
---
drivers/nvme/host/pci.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 0530432..733b4f4 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -772,16 +772,19 @@ static blk_status_t nvme_pci_setup_sgls(struct nvme_dev *dev,

static inline bool nvme_pci_use_sgls(struct nvme_dev *dev, struct request *req)
{
- struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
+ struct nvme_iod *iod;
unsigned int avg_seg_size;

- avg_seg_size = DIV_ROUND_UP(blk_rq_payload_bytes(req),
- blk_rq_nr_phys_segments(req));
-
if (!(dev->ctrl.sgls & ((1 << 0) | (1 << 1))))
return false;
+
+ iod = blk_mq_rq_to_pdu(req);
if (!iod->nvmeq->qid)
return false;
+
+ avg_seg_size = DIV_ROUND_UP(blk_rq_payload_bytes(req),
+ blk_rq_nr_phys_segments(req));
+
if (!sgl_threshold || avg_seg_size < sgl_threshold)
return false;
return true;
--
2.7.4

2018-01-11 15:45:38

by Keith Busch

Subject: Re: [PATCH] nvme-pci: calculate iod and avg_seg_size just before use them

On Thu, Jan 11, 2018 at 01:09:39PM +0800, Jianchao Wang wrote:
> The calculation of iod and avg_seg_size maybe meaningless if
> nvme_pci_use_sgls returns before uses them. So calculate
> just before use them.

The compiler will do the right thing here, but I see what you mean. I
think Christoph has some SGL improvements coming, though, that will
obviate this.

2018-01-12 01:35:50

by jianchao.wang

Subject: Re: [PATCH] nvme-pci: calculate iod and avg_seg_size just before use them

Hi Keith

Thanks for your kindly response.

On 01/11/2018 11:48 PM, Keith Busch wrote:
> On Thu, Jan 11, 2018 at 01:09:39PM +0800, Jianchao Wang wrote:
>> The calculation of iod and avg_seg_size maybe meaningless if
>> nvme_pci_use_sgls returns before uses them. So calculate
>> just before use them.
>
> The compiler will do the right thing here, but I see what you mean. I
> think Christoph has some SGL improvements coming, though, that will
> obviate this.
>
Yeah, that's great.

Thanks
Jianchao

2018-01-14 09:28:28

by Sagi Grimberg

Subject: Re: [PATCH] nvme-pci: calculate iod and avg_seg_size just before use them

>> The calculation of iod and avg_seg_size maybe meaningless if
>> nvme_pci_use_sgls returns before uses them. So calculate
>> just before use them.
>
> The compiler will do the right thing here, but I see what you mean. I
> think Christoph has some SGL improvements coming, though, that will
> obviate this.

I think that if its not coming for 4.16, it should be easy enough to
take it in.

FWIW,

Reviewed-by: Sagi Grimberg <[email protected]>