[0/8] target: fix up locking in IO paths

Message

Mike Christie Oct. 29, 2020, 6:49 a.m. UTC

The following patches made over Martin's staging branch fix some
ref counting issues I hit while testing and improves the locking
in the IO paths. To do the latter, the patches:

1. move the sess_cmd_lock to tcm_qla2xxx since it was the only
driver using the sess_cmd_list.

2. makes the execution lock/list per cpu'ish. I just allocate
nr_cpu_ids's worth of lock/lists then make sure we complete
the cmd on the cpu it was started on.

With the patches I'm seeing a 25% improvement in IOPs for small
IO tests like:

fio  --filename=/dev/sdXYZ  --direct=1 --rw=randrw --bs=4k \
--iodepth=128  --numjobs=16

with drivers like vhost (with those other patches on the list to
fix up multiple virtqueue support) and with the included loop
patch when nr hw queues is increased.

I've dropped the RFC, because Himanshu got my hw working and I've
test the qlogic patches, so please review.