From: "Ted Unangst" <tedu@tedunangst.com>
Subject: Re: Use a FIFO for the reaper
To: "Claudio Jeker" <cjeker@diehard.n-r-g.com>
Cc: "Martin Pieuchot" <mpi@grenadille.net>, tech@openbsd.org
Date: Thu, 15 May 2025 14:47:10 -0400

On 2025-05-15, Claudio Jeker wrote:
> On Thu, May 15, 2025 at 02:06:39PM -0400, Ted Unangst wrote:
> > On 2025-05-14, Martin Pieuchot wrote:
> > > Instead of adding dead threads at the head of the deadproc list insert
> > > them at the tail.
> > > 
> > > This improve latency and reduce variance when building with 24 CPUs.
> > 
> > Any theories why? I would think, if it mattered, a LIFO would be more
> > cache friendly. 
> 
> Because signaling to the parent is done in the reaper right now. So if you
> have sh executing printf and then 20 cc exit right after you want printf
> to be reaped first and not wait for 20 cc processes to cleanup.
> I think overall a fifo is fairer in that regard since the first entry can
> not starve on the queue.

oh, that makes sense.