From: Claudio Jeker <cjeker@diehard.n-r-g.com>
Subject: Re: One reaper per CPU
To: Christian Ludwig <cludwig@genua.de>
Cc: tech@openbsd.org
Date: Wed, 10 Jul 2024 17:51:26 +0200

On Wed, Jul 10, 2024 at 05:21:35PM +0200, Christian Ludwig wrote:
> Hi,
> 
> This implements one reaper process per CPU. The benefit is that we can
> switch to a safe stack (the reaper) on process teardown without the need
> to lock data structures between sched_exit() and the local reaper. That
> means the global deadproc mutex goes away. And there is also no need to
> go through idle anymore, because we know that the local reaper is not
> currently running when the dying proc enlists itself.
> 
> I have tested it lightly. It does not fall apart immediately. I do not
> see any performance regressions in my test case, which is recompiling
> the kernel over and over again, but your mileage my vary. So please give
> this some serious testing on your boxes.
> 

I thought everyone agreed that we need less reaper and not more.
All the heavy teardown done in the reaper must be moved to exit1().
After that I think having a single reaper thread is just fine (we could
even just use a task queue for cleaning up the final bits of a proc).

-- 
:wq Claudio