Re: [PATCH RFC 0/5] workqueue: add WQ_AFFN_CACHE_SHARD affinity scope

[Tejun Heo <tj@kernel.org>]

On Wed, Mar 18, 2026 at 10:51:15AM -0700, Breno Leitao wrote:
> On Tue, Mar 17, 2026 at 09:58:54AM -0400, Chuck Lever wrote:
> > On 3/17/26 7:32 AM, Breno Leitao wrote:
> > >> - How was the default shard size of 8 picked? There's a tradeoff
> > >> between the number of kworkers created and locality. Can you also
> > >> report the number of kworkers for each configuration? And is there
> > >> data on different shard sizes? It'd be useful to see how the numbers
> > >> change across e.g. 4, 8, 16, 32.
> > >
> > > The choice of 8 as the default shard size was somewhat arbitrary – it was
> > > selected primarily to generate initial data points.
> >
> > Perhaps instead of basing the sharding on a particular number of CPUs
> > per shard, why not cap the total number of shards? IIUC that is the main
> > concern about ballooning the number of kworker threads.
> 
> That's a great suggestion. I'll send a v2 that implements this approach,
> where the parameter specifies the number of shards rather than the number
> of CPUs per shard.

Woudl it make sense tho? If feels really odd to define the maximum number of
shards when contention is primarily a function of the number of CPUs banging
on the same CPU. Why would 32 cpu and 512 cpu systems have the same number
of shards?

Thanks.

-- 
tejun