Re: [PATCH v4 1/5] powerpc/smp: Enable Asym packing for cores on shared processor

[Srikar Dronamraju]

* Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> [2023-11-15 10:57:08]:

> Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx> writes:
> 
> > If there are shared processor LPARs, underlying Hypervisor can have more
> > virtual cores to handle than actual physical cores.
> >
> > Starting with Power 9, a big core (aka SMT8 core) has 2 nearly
> > independent thread groups. On a shared processors LPARs, it helps to
> > pack threads to lesser number of cores so that the overall system
> > performance and utilization improves. PowerVM schedules at a big core
> > level. Hence packing to fewer cores helps.
> >
> > For example: Lets says there are two 8-core Shared LPARs that are
> > actually sharing a 8 Core shared physical pool, each running 8 threads
> > each. Then Consolidating 8 threads to 4 cores on each LPAR would help
> > them to perform better. This is because each of the LPAR will get
> > 100% time to run applications and there will no switching required by
> > the Hypervisor.
> >
> 
> Will this patch consolidate things to first 8 threads or just the one
> Big core? /me continues to look at other patches and wonder whether 4/5
> should come before this? 

It will consolidate 1 thread per small core aka SMT domain or 2 threads per
Big core. If the load is such that there are more unbound threads than SMT
domains, asym packing will not kick-in.

4/5 would make sense only once we enable asym_packing above SMT domain.
> 
> 
> >
> > To achieve this, enable SD_ASYM_PACKING flag at CACHE, MC and DIE level
> > when the system is running in shared processor mode and has big cores.
> >
> > Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> 
> 
> -aneesh

-- 
Thanks and Regards
Srikar Dronamraju