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. Cc: linuxppc-dev <[email protected]> Cc: LKML <[email protected]> Cc: Michael Ellerman <[email protected]> Cc: Michael Neuling <[email protected]> Cc: Gautham R Shenoy <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Valentin Schneider <[email protected]> Cc: Dietmar Eggemann <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Vincent Guittot <[email protected]> Cc: Vaidyanathan Srinivasan <[email protected]> Signed-off-by: Srikar Dronamraju <[email protected]> --- arch/powerpc/include/asm/cputhreads.h | 1 - arch/powerpc/include/asm/smp.h | 13 +++++++++++++ 2 files changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/cputhreads.h b/arch/powerpc/include/asm/cputhreads.h index deb99fd6e060..98c8bd155bf9 100644 --- a/arch/powerpc/include/asm/cputhreads.h +++ b/arch/powerpc/include/asm/cputhreads.h @@ -23,7 +23,6 @@ extern int threads_per_core; extern int threads_per_subcore; extern int threads_shift; -extern bool has_big_cores; extern cpumask_t threads_core_mask; #else #define threads_per_core 1 diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h index 9cd0765633c5..d4bc28accb28 100644 --- a/arch/powerpc/include/asm/smp.h +++ b/arch/powerpc/include/asm/smp.h @@ -131,6 +131,19 @@ static inline struct cpumask *cpu_smallcore_mask(int cpu) extern int cpu_to_core_id(int cpu); +extern bool has_big_cores; + +#define cpu_smt_mask cpu_smt_mask +#ifdef CONFIG_SCHED_SMT +static inline const struct cpumask *cpu_smt_mask(int cpu) +{ + if (has_big_cores) + return per_cpu(cpu_smallcore_map, cpu); + + return per_cpu(cpu_sibling_map, cpu); +} +#endif /* CONFIG_SCHED_SMT */ + /* Since OpenPIC has only 4 IPIs, we use slightly different message numbers. * * Make sure this matches openpic_request_IPIs in open_pic.c, or what shows up -- 2.18.2
