[RFC][PATCH v1 2/3] x86/sched: Add basic support for CPU capacity scaling

Rafael J. Wysocki
2024-04-25T19:15:03Z

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

In order be able to compute the sizes of tasks consistently across all
CPUs in a hybrid system, it is necessary to provide CPU capacity scaling
information to the scheduler via arch_scale_cpu_capacity().

Add support for it via arch_cpu_scale per-CPU variables that can be set
by whoever has sufficient information on the CPU capacities.

By default, arch_cpu_scale is equal to SCHED_CAPACITY_SCALE for all
CPUs, so this change by itself is not expected to alter the current
behavior of the kernel.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
arch/x86/include/asm/topology.h | 15 +++++++++++++++
arch/x86/kernel/smpboot.c | 3 +++
2 files changed, 18 insertions(+)

Index: linux-pm/arch/x86/include/asm/topology.h
===================================================================
--- linux-pm.orig/arch/x86/include/asm/topology.h
+++ linux-pm/arch/x86/include/asm/topology.h
@@ -280,11 +280,26 @@ static inline long arch_scale_freq_capac
}
#define arch_scale_freq_capacity arch_scale_freq_capacity

+DECLARE_PER_CPU(unsigned long, arch_cpu_scale);
+
+static inline unsigned long arch_scale_cpu_capacity(int cpu)
+{
+ return READ_ONCE(per_cpu(arch_cpu_scale, cpu));
+}
+#define arch_scale_cpu_capacity arch_scale_cpu_capacity
+
+static inline void arch_set_cpu_capacity(int cpu, unsigned long cap)
+{
+ WRITE_ONCE(per_cpu(arch_cpu_scale, cpu), cap);
+}
+
extern void arch_set_max_freq_ratio(bool turbo_disabled);
extern void freq_invariance_set_perf_ratio(u64 ratio, bool turbo_disabled);

void arch_rebuild_sched_domains(void);
#else
+static inline void arch_set_cpu_capacity(int cpu, unsigned long cap) { }
+
static inline void arch_set_max_freq_ratio(bool turbo_disabled) { }
static inline void freq_invariance_set_perf_ratio(u64 ratio, bool turbo_disabled) { }

Index: linux-pm/arch/x86/kernel/smpboot.c
===================================================================
--- linux-pm.orig/arch/x86/kernel/smpboot.c
+++ linux-pm/arch/x86/kernel/smpboot.c
@@ -141,6 +141,9 @@ void arch_rebuild_sched_domains(void) {
x86_topology_update = true;
rebuild_sched_domains();
}
+
+/* CPU capacity scaling support */
+DEFINE_PER_CPU(unsigned long, arch_cpu_scale) = SCHED_CAPACITY_SCALE;
#endif

static unsigned int smpboot_warm_reset_vector_count;