On Thu, Feb 04, 2021 at 05:35:02AM -0600, Mike Christie wrote:
> The following patches made over Martin's 5.12 branches fix two
> issues:
> 
> 1. target_core_iblock plugs and unplugs the queue for every
> command. To handle this issue and handle an issue that
> vhost-scsi and loop were avoiding by adding their own workqueue,
> I added a new submission workqueue to LIO. Drivers can pass cmds
> to it, and we can then submit batches of cmds.
> 
> 2. vhost-scsi and loop on the submission side were doing a work
> per cmd and on the lio completion side it was doing a work per
> cmd. The cap on running works is 512 (max_active) and so we can
> end up end up using a lot of threads when submissions start blocking
> because they hit the block tag limit or the completion side blocks
> trying to send the cmd. In this patchset I just use a cmd list
> per session to avoid abusing the workueue layer.
> 
> The combined patchset fixes a major perf issue we've been hitting
> where IOPs is stuck at 230K when running:
> 
>     fio --filename=/dev/sda  --direct=1 --rw=randrw --bs=4k
>     --ioengine=libaio --iodepth=128  --numjobs=8 --time_based
>     --group_reporting --runtime=60
> 
> The patches in this set get me to 350K when using devices that
> have native IOPs of around 400-500K.
> 
> Note that 5.12 has some interrupt changes that my patches
> collide with. Martin's 5.12 branches had the changes so I
> based my patches on that.

For vhost-scsi:

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>