block: skip start/end time stamping for passthrough IO

block: skip start/end time stamping for passthrough IO

commit 41fa722239b4 ("blk-mq: do not include passthrough requests in I/O
accounting")' disables I/O accounting for passthrough requests. Since tools
like 'iostat' do not show anything useful for passthrough I/O, it's
wasteful to do start/end time-stamping. So do away with that.

Avoiding the time-stamping improves the I/O performance by ~7%

Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Link: https://lore.kernel.org/r/20231222101707.6921-1-kundan.kumar@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>