Re: New Default GELI kern.geom.eli.threads Value Proposal

On Thu, Jun 18, 2026 at 12:14 PM vermaden <vermaden@interia.pl> wrote:
>
> Hi.
>
> By default GELI uses all threads available on a system - like from nproc(1) output.
>
> But this 'default' is per device.
>
> I just came across one of my clients servers to 'check for possible performance improvements' and ... they had 840 GELI threads - 40 threads for each of 21 disks.
>
> This happened because client left 'kern.geom.eli.threads' on a default value.
>
> My proposal -> Change the default GELI threads value to number of physical cores.
>                -----------------------------------------------------------------
>
> So if someone has 20 physical cores with SMT - which means 40 threads - the 20 value should be used.
>
> It can be made in the source code or as intermediate step - as a config option put automatically in loader.conf(5) or sysctl.conf(5) during installation.
>
> The nproc(1) is already in Base System ... or 'kern.smp.cores' can be also used as source of information.
>
> Regards,
> vermaden

I've got a better proposal: switch geli to use a global thread pool
rather than a per-disk thread pool.  The per-disk thread pool only
really works well for laptops, which have but a single disk.  For
many-disk servers, even one thread per disk might be too much.
Instead, a global thread pool sized to nproc should in theory provide
superior performance.  And in fact, I've already implemented this
change.  However, the performance impact was not what I expected.  I
think the change helped reads but hurt writes, or maybe it was the
other way around.  Sadly, my attention got diverted to other projects
and I never returned to this one.  But I would gladly send you my
patches if you'd like to pick up where I left off.

-Alan