On Mon, Feb 14, 2022 at 01:33:24PM +0100, Paul Menzel wrote: > Dear Michal, > > > Thank you for your reply. > > Am 14.02.22 um 10:43 schrieb Michal Suchánek: > > > On Mon, Feb 14, 2022 at 07:08:07AM +0100, Paul Menzel wrote: > > > Dear PPC folks, > > > > > > > > > On the POWER8 server IBM S822LC running `ppc64_cpu --smt=off` or > > > `ppc64_cpu > > > --smt=8`, Linux 5.17-rc4 does not log anything. I would have expected a > > > message about the change in number of processing units. > > > > IIRC it was considered too noisy for systems with many CPUs and the > > message was dropped. You can always check the resulting state with > > ppc64_cpu or examining sysfs. > > Yes, simple `nproc` suffice, but I was more thinking about, that the Linux > log is often used for debugging and the changes of amount of processing > units might be good to have. `ppc64_cpu --smt=off` or `=8` seems to block > for quite some time, and each thread/processing unit seems to powered > down/on sequentially, so it takes quite some time and it blocks. So 140 > messages would indeed be quite noise. No idea how `ppc64_cpu` works, and if > it could log a message at the beginning and end.
Yes, it enables/disables threads one by one. AFAICT the kernel cannot know that ppc64_cpu will enable/disable more threads later, it can either log each or none. Rate limiting would not show the whole picture so it's not great solution either. Thanks Michal