Re: [PATCH v5 2/3] workqueue: doc: Add a note saturating the system_wq is not permitted

[Chen Ridong]

On 2024/9/26 20:49, Michal Koutný wrote:
> On Mon, Sep 23, 2024 at 11:43:51AM GMT, Chen Ridong <chenridong@xxxxxxxxxxxxxxx> wrote:
> > +  Note: If something is expected to generate a large number of concurrent
> > +  works, it should utilize its own dedicated workqueue rather than
> > +  system wq. Because this may saturate system_wq and potentially lead
> > +  to deadlock.
>
> How does "large number of concurrent" translate practically?
>
> The example with released cgroup_bpf from
>    cgroup_destroy_locked
>      cgroup_bpf_offline
> which is serialized under cgroup_mutex as argued previously. So this
> generates a single entry at a time and it wouldn't hint towards the
> creation of cgroup_bpf_destroy_wq.
>
> I reckon the argument could be something like the processing rate vs
> production rate of entry items should be such that number of active
> items is bound. But I'm not sure it's practical since users may not know
> the comparison result and they would end up always creating a dedicated
> workqueue.
>
>
> Michal

Thank you, Michal.
I think it's difficult to measure the comparison result. Actually, if 
something generates work at a high frequency, it would be better to use 
dedicated wq.

How about:
Note: If something may generate works frequently, it may saturate the 
system_wq and potentially lead to deadlock. It should utilize its own 
dedicated workqueue rather than system wq.

Best regards,
Ridong