[RFC PATCH] nvme-pci: Move the sg table allocation/free into init/exit_request

[Chaitanya Kulkarni]

On 6/28/20 3:44 AM, Baolin Wang wrote:
> Move the sg table allocation and free into the init_request() and
> exit_request(), instead of allocating sg table when queuing requests,
> which can benefit the IO performance.
> 
> Signed-off-by: Baolin Wang<baolin.wang at linux.alibaba.com>

The call to sg_init_table() uses blk_rq_nr_phys_segments in 
nvme_map_data() with this patch we are blindly allocating SG table with
NVME_MAX_SEGS, without any performance numbers it is hard to measure the 
impact.

Can you share performance numbers ?

I'm particularly interested in for IOPS/BW/CPU/USAGE/Submission latency 
and completion latency and perf numbers for the respective function in 
to determine the overall impact.