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Message-ID: <10523497.nUPlyArG6x@rjwysocki.net>
Date: Wed, 28 Aug 2024 13:47:25 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: x86 Maintainers <x86@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Ricardo Neri <ricardo.neri@...el.com>, Tim Chen <tim.c.chen@...el.com>
Subject: [PATCH v3 1/2] x86/sched: Add basic support for CPU capacity scaling
From: Rafael J. Wysocki <rafael.j.wysocki@...el.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(). Moreover,
the value returned by arch_scale_freq_capacity() for the given CPU must
correspond to the arch_scale_cpu_capacity() return value for it, or
utilization computations will be inaccurate.
Add support for it through per-CPU variables holding the capacity and
maximum-to-base frequency ratio (times SCHED_CAPACITY_SCALE) that will
be returned by arch_scale_cpu_capacity() and used by scale_freq_tick()
to compute arch_freq_scale for the current CPU, respectively.
In order to avoid adding measurable overhead for non-hybrid x86 systems,
which are the vast majority in the field, whether or not the new hybrid
CPU capacity scaling will be in effect is controlled by a static key.
This static key is set by calling arch_enable_hybrid_capacity_scale()
which also allocates memory for the per-CPU data and initializes it.
Next, arch_set_cpu_capacity() is used to set the per-CPU variables
mentioned above for each CPU and arch_rebuild_sched_domains() needs
to be called for the scheduler to realize that capacity-aware
scheduling can be used going forward.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
v2 -> v3:
* Rebase after dropping patch [1/3].
* Rename arch_set_cpu_capacity() arguments.
* Add empty line to arch_enable_hybrid_capacity_scale().
* Declare local variables in scale_freq_tick() on one line.
v1 -> v2:
* Replaces WARN_ON_ONCE() with WARN_ONCE() (2 places)
* Fix arch_enable_hybrid_capacity_scale() return value when hybrid
capacity scaling is already enabled.
* Allow arch_enable_hybrid_capacity_scale() to succeed when
frequency-invariance is not enabled.
* Fix arch_set_cpu_capacity() kerneldoc comment
* Do not disable capacity scaling in disable_freq_invariance_workfn().
* Relocate arch_hybrid_cap_scale_key definition.
---
arch/x86/include/asm/topology.h | 13 +++++
arch/x86/kernel/cpu/aperfmperf.c | 89 ++++++++++++++++++++++++++++++++++++++-
2 files changed, 100 insertions(+), 2 deletions(-)
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
@@ -282,9 +282,22 @@ static inline long arch_scale_freq_capac
}
#define arch_scale_freq_capacity arch_scale_freq_capacity
+bool arch_enable_hybrid_capacity_scale(void);
+void arch_set_cpu_capacity(int cpu, unsigned long cap, unsigned long max_cap,
+ unsigned long cap_freq, unsigned long base_freq);
+
+unsigned long arch_scale_cpu_capacity(int cpu);
+#define arch_scale_cpu_capacity arch_scale_cpu_capacity
+
extern void arch_set_max_freq_ratio(bool turbo_disabled);
extern void freq_invariance_set_perf_ratio(u64 ratio, bool turbo_disabled);
#else
+static inline bool arch_enable_hybrid_capacity_scale(void) { return false; }
+static inline void arch_set_cpu_capacity(int cpu, unsigned long cap,
+ unsigned long max_cap,
+ unsigned long cap_freq,
+ unsigned long base_freq) { }
+
static inline void arch_set_max_freq_ratio(bool turbo_disabled) { }
static inline void freq_invariance_set_perf_ratio(u64 ratio, bool turbo_disabled) { }
#endif
Index: linux-pm/arch/x86/kernel/cpu/aperfmperf.c
===================================================================
--- linux-pm.orig/arch/x86/kernel/cpu/aperfmperf.c
+++ linux-pm/arch/x86/kernel/cpu/aperfmperf.c
@@ -349,9 +349,89 @@ static DECLARE_WORK(disable_freq_invaria
DEFINE_PER_CPU(unsigned long, arch_freq_scale) = SCHED_CAPACITY_SCALE;
EXPORT_PER_CPU_SYMBOL_GPL(arch_freq_scale);
+static DEFINE_STATIC_KEY_FALSE(arch_hybrid_cap_scale_key);
+
+struct arch_hybrid_cpu_scale {
+ unsigned long capacity;
+ unsigned long freq_ratio;
+};
+
+static struct arch_hybrid_cpu_scale __percpu *arch_cpu_scale;
+
+/**
+ * arch_enable_hybrid_capacity_scale - Enable hybrid CPU capacity scaling
+ *
+ * Allocate memory for per-CPU data used by hybrid CPU capacity scaling,
+ * initialize it and set the static key controlling its code paths.
+ *
+ * Must be called before arch_set_cpu_capacity().
+ */
+bool arch_enable_hybrid_capacity_scale(void)
+{
+ int cpu;
+
+ if (static_branch_unlikely(&arch_hybrid_cap_scale_key)) {
+ WARN_ONCE(1, "Hybrid CPU capacity scaling already enabled");
+ return true;
+ }
+
+ arch_cpu_scale = alloc_percpu(struct arch_hybrid_cpu_scale);
+ if (!arch_cpu_scale)
+ return false;
+
+ for_each_possible_cpu(cpu) {
+ per_cpu_ptr(arch_cpu_scale, cpu)->capacity = SCHED_CAPACITY_SCALE;
+ per_cpu_ptr(arch_cpu_scale, cpu)->freq_ratio = arch_max_freq_ratio;
+ }
+
+ static_branch_enable(&arch_hybrid_cap_scale_key);
+
+ pr_info("Hybrid CPU capacity scaling enabled\n");
+
+ return true;
+}
+
+/**
+ * arch_set_cpu_capacity - Set scale-invariance parameters for a CPU
+ * @cpu: Target CPU.
+ * @cap: Capacity of @cpu at its maximum frequency, relative to @max_cap.
+ * @max_cap: System-wide maximum CPU capacity.
+ * @cap_freq: Frequency of @cpu corresponding to @cap.
+ * @base_freq: Frequency of @cpu at which MPERF counts.
+ *
+ * The units in which @cap and @max_cap are expressed do not matter, so long
+ * as they are consistent, because the former is effectively divided by the
+ * latter. Analogously for @cap_freq and @base_freq.
+ *
+ * After calling this function for all CPUs, call arch_rebuild_sched_domains()
+ * to let the scheduler know that capacity-aware scheduling can be used going
+ * forward.
+ */
+void arch_set_cpu_capacity(int cpu, unsigned long cap, unsigned long max_cap,
+ unsigned long cap_freq, unsigned long base_freq)
+{
+ if (static_branch_likely(&arch_hybrid_cap_scale_key)) {
+ WRITE_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->capacity,
+ div_u64(cap << SCHED_CAPACITY_SHIFT, max_cap));
+ WRITE_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->freq_ratio,
+ div_u64(cap_freq << SCHED_CAPACITY_SHIFT, base_freq));
+ } else {
+ WARN_ONCE(1, "Hybrid CPU capacity scaling not enabled");
+ }
+}
+
+unsigned long arch_scale_cpu_capacity(int cpu)
+{
+ if (static_branch_unlikely(&arch_hybrid_cap_scale_key))
+ return READ_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->capacity);
+
+ return SCHED_CAPACITY_SCALE;
+}
+EXPORT_SYMBOL_GPL(arch_scale_cpu_capacity);
+
static void scale_freq_tick(u64 acnt, u64 mcnt)
{
- u64 freq_scale;
+ u64 freq_scale, freq_ratio;
if (!arch_scale_freq_invariant())
return;
@@ -359,7 +439,12 @@ static void scale_freq_tick(u64 acnt, u6
if (check_shl_overflow(acnt, 2*SCHED_CAPACITY_SHIFT, &acnt))
goto error;
- if (check_mul_overflow(mcnt, arch_max_freq_ratio, &mcnt) || !mcnt)
+ if (static_branch_unlikely(&arch_hybrid_cap_scale_key))
+ freq_ratio = READ_ONCE(this_cpu_ptr(arch_cpu_scale)->freq_ratio);
+ else
+ freq_ratio = arch_max_freq_ratio;
+
+ if (check_mul_overflow(mcnt, freq_ratio, &mcnt) || !mcnt)
goto error;
freq_scale = div64_u64(acnt, mcnt);
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