Re: [PATCH v2 0/5] workqueue: Introduce a sharded cache affinity scope

[Tejun Heo]

Hello,

On Mon, Mar 23, 2026 at 02:04:57PM -0400, Chuck Lever wrote:
> > I don't see why the cores-per-shard approach wouldn't scale down
> > effectively.
> 
> Sharding the UNBOUND pool is fine. But with a fixed cores-per-shard
> ratio of 8, it doesn't scale down to smaller systems.

You aren't making a lot of sense. Contention is primarily the function of
the number of CPUs competing, not inverse of how many cores are in the LLC.

> A shard size of 2 clearly won't scale properly to hundreds of cores. A
> varying default cores-per-shard ratio would help scaling in both
> directions, without having to manually tune.

If your workload is bottlenecked on pool lock on small machines, the right
course of action is either making the offending workqueue per-cpu or
configure the unbound workqueue for that specific use case. That's why it's
progrmatically configurable in the first place.

Thanks.

-- 
tejun