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Date: Thu, 16 Oct 2008 17:15:58 +0530
From: Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Cc: a.p.zijlstra@...llo.nl, ego@...ibm.com, tglx@...utronix.de,
mingo@...e.hu, andi@...stfloor.org, venkatesh.pallipadi@...el.com,
vatsa@...ux.vnet.ibm.com, arjan@...radead.org,
arun@...ux.vnet.ibm.com
Subject: [RFC PATCH 1/4] timers: Sysfs hook to enable timer migration
This patch creates the necessary sysfs interface for timer migration.
The interface is located at /sys/devices/system/cpu/cpuX/timer_migration
These sysfs entries are initialized to their respective cpu ids.
This represents the no timer migration state.
By echoing a target cpu number we can enable migration for that cpu.
Echo a target cpu number to the per-cpu sysfs entry and all timers
are migrated to that cpu, instead of choosing cpu0 by default.
e.g. echo 4 > /sys/devices/system/cpu/cpu1/timer_migration
this would move all regular and hrtimers from cpu1 to cpu4.
Signed-off-by: Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
---
drivers/base/cpu.c | 42 ++++++++++++++++++++++++++++++++++++++++++
include/linux/timer.h | 2 ++
2 files changed, 44 insertions(+)
Index: linux-2.6.27/drivers/base/cpu.c
===================================================================
--- linux-2.6.27.orig/drivers/base/cpu.c
+++ linux-2.6.27/drivers/base/cpu.c
@@ -20,6 +20,43 @@ EXPORT_SYMBOL(cpu_sysdev_class);
static DEFINE_PER_CPU(struct sys_device *, cpu_sys_devices);
+DEFINE_PER_CPU(int, enable_timer_migration);
+
+/* This function initializes sysfs entries for enabling timer migration.
+ * Each per_cpu enable_timer_migration is initialized to its cpu_id.
+ * By echo-ing a value other than its cpu_id will set that as the target cpu
+ * to which the timers are to be migrated to.
+ */
+void initialize_timer_migration_sysfs(void)
+{
+ int cpu;
+ for_each_possible_cpu(cpu)
+ per_cpu(enable_timer_migration, cpu) = cpu;
+}
+
+static ssize_t timer_migration_show(struct sys_device *dev, char *buf)
+{
+ struct cpu *cpu = container_of(dev, struct cpu, sysdev);
+ return sprintf(buf, "%u\n", per_cpu(enable_timer_migration,
+ cpu->sysdev.id));
+}
+static ssize_t
+timer_migration_store(struct sys_device *dev, const char *buf, size_t count)
+{
+ struct cpu *cpu = container_of(dev, struct cpu, sysdev);
+ ssize_t ret = -EINVAL;
+ int target_cpu;
+ sscanf(buf, "%d", &target_cpu);
+ if (cpu_online(target_cpu)) {
+ ret = count;
+ per_cpu(enable_timer_migration, cpu->sysdev.id) = target_cpu;
+ }
+
+ return ret;
+}
+static SYSDEV_ATTR(timer_migration, 0644,
+ timer_migration_show, timer_migration_store);
+
#ifdef CONFIG_HOTPLUG_CPU
static ssize_t show_online(struct sys_device *dev, struct sysdev_attribute *attr,
char *buf)
@@ -177,6 +214,11 @@ int __cpuinit register_cpu(struct cpu *c
if (!error)
error = sysdev_create_file(&cpu->sysdev, &attr_crash_notes);
#endif
+
+ if (!error) {
+ error = sysdev_create_file(&cpu->sysdev, &attr_timer_migration);
+ initialize_timer_migration_sysfs();
+ }
return error;
}
Index: linux-2.6.27/include/linux/timer.h
===================================================================
--- linux-2.6.27.orig/include/linux/timer.h
+++ linux-2.6.27/include/linux/timer.h
@@ -187,3 +187,5 @@ unsigned long round_jiffies(unsigned lon
unsigned long round_jiffies_relative(unsigned long j);
#endif
+
+DECLARE_PER_CPU(int, enable_timer_migration);
--
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