Re: [RFC PATCH] scsi: scsi_transport_srp: Move long delayed work on system_dfl_long_wq

[Bart Van Assche <bvanassche@acm.org>]

On 5/7/26 7:34 AM, Marco Crivellari wrote:
> Currently the code enqueue work items using {queue|mod}_delayed_work(),
> using system_long_wq. This workqueue should be used when long works are
> expected and it is a per-cpu workqueue.
> 
> The function(s) end up calling __queue_delayed_work(), which set a global
> timer that could fire anywhere, enqueuing the work where the timer fired.
> 
> Unbound works could benefit from scheduler task placement, to optimize
> performance and power consumption. Long work shouldn't stick to a single
> CPU.
> 
> Recently, a new unbound workqueue specific for long running work has
> been added:
> 
>      c116737e972e ("workqueue: Add system_dfl_long_wq for long unbound works")
> 
> Since the workqueue work doesn't rely on per-cpu variables, there is no
> obvious reason that justify the use of a per-cpu workqueue. So change
> system_long_wq with system_dfl_long_wq so that the work may benefit from
> scheduler task placement.

This looks like unnecessary churn to me. The motivation for the
introduction of system_dfl_long_wq seems very weak to me. Wouldn't we
all be better off if commit c116737e972e would be reverted and if the
behavior of system_long_wq would be modified from per-CPU into unbound?

Thanks,

Bart.