Re: [PATCH net-next v5] Add support to set napi threaded for individual napi

[Joe Damato <jdamato@fastly.com>]

On Fri, Apr 25, 2025 at 05:37:43PM -0700, Jakub Kicinski wrote:
> On Fri, 25 Apr 2025 15:52:30 -0700 Samiullah Khawaja wrote:
> > > Probably need a maintainer to weigh-in on what the preferred
> > > behavior is. Maybe there's a reason the thread isn't killed.  
> > +1
> > 
> > I think the reason behind it not being killed is because the user
> > might have already done some configuration using the PID and if the
> > kthread was removed, the user would have to do that configuration
> > again after enable/disable. But I am just speculating. I will let the
> > maintainers weigh-in as you suggested.
> 
> I haven't looked at the code, but I think it may be something more
> trivial, namely that napi_enable() return void, so it can't fail.
> Also it may be called under a spin lock.

If you don't mind me asking: what do you think at a higher level
on the discussion about threaded NAPI being disabled?

It seems like the current behavior is:
  - If you write 1 to the threaded NAPI sysfs path, kthreads are
    kicked off and start running.

  - If you write 0, the threads are not killed but don't do any
    processing and their pids are still exported in netlink.

I was arguing in favor of disabling threading means the thread is
killed and the pid is no longer exported (as a side effect) because
it seemed weird to me that the netlink output would say:

   pid: 1234
   threaded: 0

In the current implementation.