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Subject[PATCH v3 2/6] drivers/cpufreq: implement init_cpu_capacity_default()
Date
To get default values for CPUs capacity we profile a simple (bogus)
integer benchmark on such CPUs; then we normalize results to 1024
(highest capacity in the system).

Architectures that want this during boot have to define a weak function
(arch_wants_init_cpu_capacity) to return true.

Also, kernel has to boot with init_cpu_capacity parameter if profiling
is needed, as it can be expensive and might add ~1 sec to boot time.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
---
Changes since v1:
- add kernel command line parameter to enable profiling
- add define for max trials

Documentation/kernel-parameters.txt | 4 +
arch/arm/kernel/topology.c | 2 +-
arch/arm64/kernel/topology.c | 12 +++
drivers/cpufreq/Makefile | 2 +-
drivers/cpufreq/cpufreq.c | 1 +
drivers/cpufreq/cpufreq_capacity.c | 174 ++++++++++++++++++++++++++++++++++++
include/linux/cpufreq.h | 2 +
7 files changed, 195 insertions(+), 2 deletions(-)
create mode 100644 drivers/cpufreq/cpufreq_capacity.c

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 87d40a7..fad2b89 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1570,6 +1570,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.

initrd= [BOOT] Specify the location of the initial ramdisk

+ init_cpu_capacity
+ [KNL,ARM] Enables dynamic CPUs capacity benchmarking
+ at boot.
+
inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
Format: <irq>

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index ec279d1..c9c87a5 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -47,7 +47,7 @@ unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
return per_cpu(cpu_scale, cpu);
}

-static void set_capacity_scale(unsigned int cpu, unsigned long capacity)
+void set_capacity_scale(unsigned int cpu, unsigned long capacity)
{
per_cpu(cpu_scale, cpu) = capacity;
}
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 694f6de..3b75d63 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -23,6 +23,18 @@
#include <asm/cputype.h>
#include <asm/topology.h>

+static DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
+
+unsigned long arm_arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
+{
+ return per_cpu(cpu_scale, cpu);
+}
+
+void set_capacity_scale(unsigned int cpu, unsigned long capacity)
+{
+ per_cpu(cpu_scale, cpu) = capacity;
+}
+
static int __init get_cpu_for_node(struct device_node *node)
{
struct device_node *cpu_node;
diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
index 9e63fb1..c4025fd 100644
--- a/drivers/cpufreq/Makefile
+++ b/drivers/cpufreq/Makefile
@@ -1,5 +1,5 @@
# CPUfreq core
-obj-$(CONFIG_CPU_FREQ) += cpufreq.o freq_table.o
+obj-$(CONFIG_CPU_FREQ) += cpufreq.o freq_table.o cpufreq_capacity.o

# CPUfreq stats
obj-$(CONFIG_CPU_FREQ_STAT) += cpufreq_stats.o
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index e979ec7..b22afe8 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2440,6 +2440,7 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
}

register_hotcpu_notifier(&cpufreq_cpu_notifier);
+ cpufreq_init_cpu_capacity();
pr_debug("driver %s up and running\n", driver_data->name);

out:
diff --git a/drivers/cpufreq/cpufreq_capacity.c b/drivers/cpufreq/cpufreq_capacity.c
new file mode 100644
index 0000000..e54310b
--- /dev/null
+++ b/drivers/cpufreq/cpufreq_capacity.c
@@ -0,0 +1,174 @@
+/*
+ * Default CPU capacity calculation for u-arch invariance
+ *
+ * Copyright (C) 2015 ARM Ltd.
+ * Juri Lelli <juri.lelli@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed "as is" WITHOUT ANY WARRANTY of any
+ * kind, whether express or implied; without even the implied warranty
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+#include <linux/cpufreq.h>
+#include <linux/sched.h>
+
+#define MAX_TRIALS 10 /* how many times benchmark is executed */
+static unsigned long long elapsed[NR_CPUS];
+
+/*
+ * Don't let compiler optimize following two functions; we want to avoid any
+ * microarchitecture specific optimization that compiler would do and favour
+ * one CPU vs. another. Also, my_int_sqrt is cut-and-paste from
+ * lib/int_sqrt.c.
+ */
+static unsigned long __attribute__((optimize("O0")))
+my_int_sqrt(unsigned long x)
+{
+ unsigned long b, m, y = 0;
+
+ if (x <= 1)
+ return x;
+
+ m = 1UL << (BITS_PER_LONG - 2);
+ while (m != 0) {
+ b = y + m;
+ y >>= 1;
+
+ if (x >= b) {
+ x -= b;
+ y += m;
+ }
+ m >>= 2;
+ }
+
+ return y;
+}
+
+static unsigned long __attribute__((optimize("O0")))
+bogus_bench(void)
+{
+ unsigned long i, res;
+
+ for (i = 0; i < 100000; i++)
+ res = my_int_sqrt(i);
+
+ return res;
+}
+
+static int run_bogus_benchmark(int cpu)
+{
+ int ret, trials = MAX_TRIALS;
+ u64 begin, end, sample, mean = 0, count = 0;
+ unsigned long res;
+
+ ret = set_cpus_allowed_ptr(current, cpumask_of(cpu));
+ if (ret) {
+ pr_warn("%s: failed to set allowed ptr\n", __func__);
+ return -EINVAL;
+ }
+
+ while (trials--) {
+ begin = local_clock();
+ res = bogus_bench();
+ end = local_clock();
+ sample = end - begin;
+
+ mean = mean * count + sample;
+ mean = div64_u64(mean, ++count);
+ pr_debug("%s: cpu=%d begin=%llu end=%llu"
+ " sample=%llu mean=%llu count=%llu res=%lu\n",
+ __func__, cpu, begin, end, sample,
+ mean, count, res);
+ }
+ elapsed[cpu] = mean;
+
+ ret = set_cpus_allowed_ptr(current, cpu_active_mask);
+ if (ret) {
+ pr_warn("%s: failed to set allowed ptr\n", __func__);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+bool __weak arch_wants_init_cpu_capacity(void)
+{
+ return false;
+}
+
+void __weak set_capacity_scale(int cpu, unsigned long capacity) { }
+
+static __read_mostly bool init_cpu_capacity_enabled;
+
+static int __init init_cpu_capacity_setup(char *str)
+{
+ init_cpu_capacity_enabled = true;
+
+ return 0;
+}
+early_param("init_cpu_capacity", init_cpu_capacity_setup);
+
+void cpufreq_init_cpu_capacity(void)
+{
+ int cpu, fcpu;
+ unsigned long long elapsed_min = ULLONG_MAX;
+ unsigned int curr_min, curr_max;
+ struct cpufreq_policy *policy;
+
+ if (!arch_wants_init_cpu_capacity() || !init_cpu_capacity_enabled)
+ return;
+
+ for_each_possible_cpu(cpu) {
+ policy = cpufreq_cpu_get(cpu);
+ if (IS_ERR_OR_NULL(policy))
+ return;
+
+ /*
+ * We profile only first CPU of each frequency domain;
+ * and use that value as capacity of every CPU in the domain.
+ */
+ fcpu = cpumask_first(policy->related_cpus);
+ if (cpu != fcpu) {
+ elapsed[cpu] = elapsed[fcpu];
+ cpufreq_cpu_put(policy);
+ continue;
+ }
+
+ down_write(&policy->rwsem);
+ curr_min = policy->user_policy.min;
+ curr_max = policy->user_policy.max;
+ policy->user_policy.min = policy->cpuinfo.max_freq;
+ policy->user_policy.max = policy->cpuinfo.max_freq;
+ up_write(&policy->rwsem);
+ cpufreq_cpu_put(policy);
+ cpufreq_update_policy(cpu);
+
+ run_bogus_benchmark(cpu);
+ if (elapsed[cpu] < elapsed_min)
+ elapsed_min = elapsed[cpu];
+ pr_debug("%s: cpu=%d elapsed=%llu (min=%llu)\n",
+ __func__, cpu, elapsed[cpu], elapsed_min);
+
+ policy = cpufreq_cpu_get(cpu);
+ down_write(&policy->rwsem);
+ policy->user_policy.min = curr_min;
+ policy->user_policy.max = curr_max;
+ up_write(&policy->rwsem);
+ cpufreq_cpu_put(policy);
+ cpufreq_update_policy(cpu);
+ }
+
+ for_each_possible_cpu(cpu) {
+ unsigned long capacity;
+
+ capacity = div64_u64((elapsed_min << 10), elapsed[cpu]);
+ pr_debug("%s: CPU%d capacity=%lu\n", __func__, cpu, capacity);
+ set_capacity_scale(cpu, capacity);
+ }
+
+ pr_info("dynamic CPUs capacity installed\n");
+}
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 88a4215..9924351 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -419,6 +419,8 @@ static inline unsigned long cpufreq_scale(unsigned long old, u_int div,
#endif
}

+void cpufreq_init_cpu_capacity(void);
+
/*********************************************************************
* CPUFREQ GOVERNORS *
*********************************************************************/
--
2.7.0
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