x86: sched: Provide arch implementations using aperf/mperf

APERF/MPERF support for cpu_power.

APERF/MPERF is arch defined to be a relative scale of work capacity
per logical cpu, this is assumed to include SMT and Turbo mode.

APERF/MPERF are specified to both reset to 0 when either counter
wraps, which is highly inconvenient, since that'll give a blimp
when that happens. The manual specifies writing 0 to the counters
after each read, but that's 1) too expensive, and 2) destroys the
possibility of sharing these counters with other users, so we live
with the blimp - the other existing user does too.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 55 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/sched.c b/arch/x86/kernel/cpu/sched.c
new file mode 100644
index 000000000000..6c00a8f3cce5
--- /dev/null
+++ b/arch/x86/kernel/cpu/sched.c
@@ -0,0 +1,55 @@
+#include <linux/sched.h>
+#include <linux/math64.h>
+#include <linux/percpu.h>
+#include <linux/irqflags.h>
+
+#include <asm/cpufeature.h>
+#include <asm/processor.h>
+
+#ifdef CONFIG_SMP
+
+static DEFINE_PER_CPU(struct aperfmperf, old_perf);
+
+static unsigned long scale_aperfmperf(void)
+{
+        struct aperfmperf val, *old = &__get_cpu_var(old_perf);
+        unsigned long ratio, flags;
+
+        local_irq_save(flags);
+        get_aperfmperf(&val);
+        local_irq_restore(flags);
+
+        ratio = calc_aperfmperf_ratio(old, &val);
+        *old = val;
+
+        return ratio;
+}
+
+unsigned long arch_scale_freq_power(struct sched_domain *sd, int cpu)
+{
+        /*
+         * do aperf/mperf on the cpu level because it includes things
+         * like turbo mode, which are relevant to full cores.
+         */
+        if (boot_cpu_has(X86_FEATURE_APERFMPERF))
+                return scale_aperfmperf();
+
+        /*
+         * maybe have something cpufreq here
+         */
+
+        return default_scale_freq_power(sd, cpu);
+}
+
+unsigned long arch_scale_smt_power(struct sched_domain *sd, int cpu)
+{
+        /*
+         * aperf/mperf already includes the smt gain
+         */
+        if (boot_cpu_has(X86_FEATURE_APERFMPERF))
+                return SCHED_LOAD_SCALE;
+
+        return default_scale_smt_power(sd, cpu);
+}
+
+#endif