[systemd-devel] question on special configuration case

[Greg KH]

On Wed, Jun 08, 2016 at 02:04:48AM +0000, Hebenstreit, Michael wrote:
> > What processes are showing up in your count?  Perhaps it's just a
> > bug that needs to be fixed.
> /bin/dbus-daemon
> /usr/lib/systemd/systemd-journald
> /usr/lib/systemd/systemd-logind
> 
> I understand from the previous mails those are necessary to make
> systemd work - but here they are doing nothing more than talking to
> each other!

Really?  No journal messages are getting created at all?  No users
logging in/out?  What does strace show on those processes?

> > That what "most" other system designers in your situation do :)
> Unfortunately I cannot reserve a CPU for OS - I'd like to, but the app
> developers insist to use all 254 cores available

So you are hurting all 253 cores because you can't spare 1?  If you do
the math I think you will find you will get increased throughput.  But
what do I know... :)

> > Your kernel is eating more CPU time than those 1s numbers, why you
> > aren't complaining about that seems strange to me :)
> I also check kernel - last time I look on RH6 all kernel threads
> taking up clock ticks were actually doing work ^^ No time yet to do
> the same on RH7 kernel

Again, that's not the issue, you can't see the time the kernel is using
to do its work, but it is there (interrupts, scheduling, housekeeping,
etc.)  So get it out of the way entirely and see how much faster your
application runs without it even present on those cpus, if you really
have cpu bound processes.  That's what the feature was made for, people
in your situation, to ignore it and try to go after something else seems
very strange to me.

greg k-h