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

Aneesh Kumar K.V
2023-11-15T05:32:15Z

Srikar Dronamraju <srikar@linux.vnet.ibm.com> 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 <srikar@linux.vnet.ibm.com>

-aneesh