Re: [PATCH 2/2] powerpc/topology: Override cpu_smt_mask

From: peterz
Date: Tue Aug 04 2020 - 06:48:53 EST

On Tue, Aug 04, 2020 at 09:03:07AM +0530, Srikar Dronamraju wrote:
> On Power9 a pair of cores can be presented by the firmware as a big-core
> for backward compatibility reasons, with 4 threads per (small) core and 8
> threads per big-core. cpu_smt_mask() should generally point to the cpu mask
> of the (small)core.
> In order to maintain userspace backward compatibility (with Power8 chips in
> case of Power9) in enterprise Linux systems, the topology_sibling_cpumask
> has to be set to big-core. Hence override the default cpu_smt_mask() to be
> powerpc specific allowing for better scheduling behaviour on Power.

Why does Linux userspace care about this?