* Peter Zijlstra [off-list ref] [2023-10-19 09:48:28]:

On Thu, Oct 19, 2023 at 03:38:40PM +1100, Michael Ellerman wrote:

quoted

Srikar Dronamraju [off-list ref] writes:

quoted

If there are shared processor LPARs, underlying Hypervisor can have more
virtual cores to handle than actual physical cores.

Starting with Power 9, a core has 2 nearly independent thread groups.

You need to be clearer here that you're talking about "big cores", not
SMT4 cores as seen on bare metal systems.

What is a 'big core' ? I'm thinking big.LITTLE, but I didn't think Power
went that route (yet?).. help?

Each independent thread group acts as a SMT4 core or a small core. A set of
2 thread groups form a SMT8 core aka big core. PowerVM aka pHYp schedules
at a big core granularity

So if we have 2 LPARS, each spanning 2 big cores, aka 16 CPUs, and if at
somepoint, each LPAR has only 2 threads to run, we are exploring if we can
run both the threads on just one big core, so that PhyP can schedule both
LPARS at the same time and avoid having to switch/multiplex between these
two LPARS.

-- 
Thanks and Regards
Srikar Dronamraju