On Tue, Aug 04, 2020 at 09:03:06AM +0530, Srikar Dronamraju wrote: > cpu_smt_mask tracks topology_sibling_cpumask. This would be good for > most architectures. One of the users of cpu_smt_mask(), would be to > identify idle-cores. On Power9, a pair of cores can be presented by the > firmware as a big-core for backward compatibility reasons. > > In order to maintain userspace backward compatibility with previous > versions of processor, (since Power8 had SMT8 cores), Power9 onwards there > is option to the firmware to advertise a pair of SMT4 cores as a fused > cores (referred to as the big_core mode in the Linux Kernel). On Power9 > this pair shares the L2 cache as well. However, from the scheduler's point > of view, a core should be determined by SMT4. The load-balancer already > does this. Hence allow PowerPc architecture to override the default > cpu_smt_mask() to point to the SMT4 cores in a big_core mode.
I'm utterly confused. Why can't you set your regular siblings mask to the smt4 thing? Who cares about the compat stuff, I thought that was an LPAR/AIX thing.