From: Claudio Jeker <cjeker@diehard.n-r-g.com>
Subject: Re: Unlock sysctl kern.maxclusters
To: Theo de Raadt <deraadt@openbsd.org>
Cc: Vitaliy Makkoveev <mvs@openbsd.org>, Mark Kettenis <mark.kettenis@xs4all.nl>, Alexander Bluhm <bluhm@openbsd.org>, tech@openbsd.org
Date: Tue, 3 Jun 2025 20:28:19 +0200

On Tue, Jun 03, 2025 at 08:15:10AM -0600, Theo de Raadt wrote:
> > Why do we need to move "nmbclust * MCLBYTES" to the hot path
> > and use it instead of pre-calculated `mbuf_mem_limit'?
> 
> I do not think a multiplication is hot, compared to userland being able
> to do a sysctl() operation and grab a mutex against the mbuf layer.

MCLBYTES is a power of two. So this hot multiplication will be reduced to
a shift instruction which is probably not even noticable. 

-- 
:wq Claudio