[RFC PATCH 0/5] nvme: reduce repetitive calls in fast path

[Chaitanya Kulkarni]

On 7/7/20 00:11, Christoph Hellwig wrote:
> blk_rq_nr_phys_segments is pretty trivial - just a branch and struct
> field access.  Does this make any kind of difference?

I've not seen any difference, on the code level host side adds the same
additional multiple checks (fc(3)/rdam(1)/tcp(1)) and if the device on
the target is nvme controller (nvme-pci with SGL 3 additional checks)
the same check will get repeated (host + pci) in host-target fast path.

In this case having same multiple checks is not bringing us anything
either since rq_nr_phys_seg is not changed once we setup the command in
nvme_setup_cmd() unless I miss something.