From: "Srivatsa S. Bhat" <srivatsa.b...@linux.vnet.ibm.com>
On POWER systems, the CPU frequency is controlled at a core-level and
hence we need to serialize so that only one of the threads in the core
switches the core's frequency at a time.
Using a global mutex lock would needlessly serialize _all_ frequency
transitions in the system (across all cores). So introduce per-core
locking to enable finer-grained synchronization and thereby enhance
the speed and responsiveness of the cpufreq driver to varying workload
demands.
The design of per-core locking is very simple and straight-forward: we
first define a Per-CPU lock and use the ones that belongs to the first
thread sibling of the core.
cpu_first_thread_sibling() macro is used to find the *common* lock for
all thread siblings belonging to a core.
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
Signed-off-by: Vaidyanathan Srinivasan <sva...@linux.vnet.ibm.com>
Signed-off-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
---
drivers/cpufreq/powernv-cpufreq.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/drivers/cpufreq/powernv-cpufreq.c
b/drivers/cpufreq/powernv-cpufreq.c
index 4cad727..4c2e8ca 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -24,8 +24,15 @@
#include <linux/of.h>
#include <asm/cputhreads.h>
-/* FIXME: Make this per-core */
-static DEFINE_MUTEX(freq_switch_mutex);
+/* Per-Core locking for frequency transitions */
+static DEFINE_PER_CPU(struct mutex, freq_switch_lock);
+
+#define lock_core_freq(cpu) \
+ mutex_lock(&per_cpu(freq_switch_lock,\
+ cpu_first_thread_sibling(cpu)));
+#define unlock_core_freq(cpu) \
+ mutex_unlock(&per_cpu(freq_switch_lock,\
+ cpu_first_thread_sibling(cpu)));
#define POWERNV_MAX_PSTATES 256
@@ -233,7 +240,7 @@ static int powernv_cpufreq_target(struct cpufreq_policy
*policy,
freqs.new = powernv_freqs[new_index].frequency;
freqs.cpu = policy->cpu;
- mutex_lock(&freq_switch_mutex);
+ lock_core_freq(policy->cpu);
cpufreq_notify_transition(policy, &freqs, CPUFREQ_PRECHANGE);
pr_debug("setting frequency for cpu %d to %d kHz index %d pstate %d",
@@ -245,7 +252,7 @@ static int powernv_cpufreq_target(struct cpufreq_policy
*policy,
rc = powernv_set_freq(policy->cpus, new_index);
cpufreq_notify_transition(policy, &freqs, CPUFREQ_POSTCHANGE);
- mutex_unlock(&freq_switch_mutex);
+ unlock_core_freq(policy->cpu);
return rc;
}
@@ -262,7 +269,7 @@ static struct cpufreq_driver powernv_cpufreq_driver = {
static int __init powernv_cpufreq_init(void)
{
- int rc = 0;
+ int cpu, rc = 0;
/* Discover pstates from device tree and init */
@@ -272,6 +279,10 @@ static int __init powernv_cpufreq_init(void)
pr_info("powernv-cpufreq disabled\n");
return rc;
}
+ /* Init per-core mutex */
+ for_each_possible_cpu(cpu) {
+ mutex_init(&per_cpu(freq_switch_lock, cpu));
+ }
rc = cpufreq_register_driver(&powernv_cpufreq_driver);
return rc;
--
1.8.3.1
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