Srikar Dronamraju <[email protected]> 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?
>
> 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 <[email protected]>
-aneesh
* Aneesh Kumar K.V <[email protected]> [2023-11-15 10:57:08]:
> Srikar Dronamraju <[email protected]> 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 <[email protected]>
>
>
> -aneesh
--
Thanks and Regards
Srikar Dronamraju