From: Srikar Dronamraju Date: Fri, 7 Aug 2020 07:45:16 +0000 (+0530) Subject: sched/topology: Allow archs to override cpu_smt_mask X-Git-Tag: io_uring-5.10-2020-10-20~30^2~95 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=3babbe447d76ac2919ec4d0eb3b0adfb22f5b03c;p=linux-block.git sched/topology: Allow archs to override cpu_smt_mask 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 SMT4 cores can be presented by the firmware as a SMT8 core for backward compatibility reasons. powerpc allows LPARs to be live migrated from Power8 to Power9. Do note Power8 had only SMT8 cores. Existing software which has been developed/configured for Power8 would expect to see SMT8 core. Maintaining the illusion of SMT8 core is a requirement to make that work. In order to maintain above userspace backward compatibility with previous versions of processor, Power9 onwards there is option to the firmware to advertise a pair of SMT4 cores as a fused cores aka SMT8 core. 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, since its a completely independent unit of compute. Hence allow powerpc architecture to override the default cpu_smt_mask() to point to the SMT4 cores in a SMT8 mode. This will ensure the scheduler is always given the right information. Acked-by: Peter Zijlstra (Intel) Signed-off-by: Srikar Dronamraju Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200807074517.27957-1-srikar@linux.vnet.ibm.com --- diff --git a/include/linux/topology.h b/include/linux/topology.h index 608fa4aadf0e..ad03df1cc266 100644 --- a/include/linux/topology.h +++ b/include/linux/topology.h @@ -198,7 +198,7 @@ static inline int cpu_to_mem(int cpu) #define topology_die_cpumask(cpu) cpumask_of(cpu) #endif -#ifdef CONFIG_SCHED_SMT +#if defined(CONFIG_SCHED_SMT) && !defined(cpu_smt_mask) static inline const struct cpumask *cpu_smt_mask(int cpu) { return topology_sibling_cpumask(cpu);