On 2024-01-29 23:11:47 [-1000], Tejun Heo wrote:

Hello,

Hi,

As suggested, this patchset implements BH workqueues which are like regular
workqueues but executes work items in the BH (softirq) context and converts
several tasklet users.

- The name bh is used instead of the suggested atomic as it's more in line
  with widely used execution context interface - local_bh_enable/disable()
  and friends.

- The system default BH workqueues - system_bh_wq and system_bh_highpri_wq -
  are provided. As queue-wide flushing doesn't exist in tasklet, all
  existing tasklet users should be able to use the system BH workqueues
  without creating their own.

- BH workqueues currently use tasklet to run the work items to avoid
  priority inversions involving tasklet_hi and WQ_BH | WQ_HIGHPRI. Once all
  tasklet users are converted, tasklet code can be removed and BH workqueues
  can take over its softirqs.

If one context creates multiple work item which are then moved to
tasklet I don't see the difference vs workqueue with a bh_disable()
around it.
Looking at the USB changes, I would prefer to see it converted to
threaded interrupts instead of using tasklet or workqueue. Both
approaches (current tasklet, suggested workqueue) lose the original
context where the request was created. Having threaded interrupts would
allow to keep everything in the same "context" so you could prioritize
according to your needs.

Sebastian