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SubjectRe: [PATCH RFC] pm_qos_requirement might sleep
From: John Kacur <jkacur at gmail dot com>

Patch to make PM_QOS and CPU_IDLE play nicer when ran with the
RT-Preempt kernel. CPU_IDLE polls the target_value's of some of the
pm_qos parameters from the idle loop causing sleeping locking
warnings. Changing the target_value to an atomic avoids this issue.

Signed-off-by: mark gross <mgross@linux.intel.com>

Thanks,

--mgross


Remove the spinlock in pm_qos_requirement by making target_value an atomic type.
This is necessary for real-time since pm_qos_requirement is called by idle and
cannot be allowed to sleep.
Signed-off-by: John Kacur <jkacur at gmail dot com>

Index: linux-2.6/kernel/pm_qos_params.c
===================================================================
--- linux-2.6.orig/kernel/pm_qos_params.c 2008-08-08 07:52:01.000000000 -0700
+++ linux-2.6/kernel/pm_qos_params.c 2008-08-28 12:14:55.000000000 -0700
@@ -43,7 +43,7 @@
#include <linux/uaccess.h>

/*
- * locking rule: all changes to target_value or requirements or notifiers lists
+ * locking rule: all changes to requirements or notifiers lists
* or pm_qos_object list and pm_qos_objects need to happen with pm_qos_lock
* held, taken with _irqsave. One lock to rule them all
*/
@@ -66,7 +66,7 @@
struct miscdevice pm_qos_power_miscdev;
char *name;
s32 default_value;
- s32 target_value;
+ atomic_t target_value;
s32 (*comparitor)(s32, s32);
};

@@ -77,7 +77,7 @@
.notifiers = &cpu_dma_lat_notifier,
.name = "cpu_dma_latency",
.default_value = 2000 * USEC_PER_SEC,
- .target_value = 2000 * USEC_PER_SEC,
+ .target_value = ATOMIC_INIT(2000 * USEC_PER_SEC),
.comparitor = min_compare
};

@@ -87,7 +87,7 @@
.notifiers = &network_lat_notifier,
.name = "network_latency",
.default_value = 2000 * USEC_PER_SEC,
- .target_value = 2000 * USEC_PER_SEC,
+ .target_value = ATOMIC_INIT(2000 * USEC_PER_SEC),
.comparitor = min_compare
};

@@ -99,7 +99,7 @@
.notifiers = &network_throughput_notifier,
.name = "network_throughput",
.default_value = 0,
- .target_value = 0,
+ .target_value = ATOMIC_INIT(0),
.comparitor = max_compare
};

@@ -150,11 +150,11 @@
extreme_value = pm_qos_array[target]->comparitor(
extreme_value, node->value);
}
- if (pm_qos_array[target]->target_value != extreme_value) {
+ if (atomic_read(&pm_qos_array[target]->target_value) != extreme_value) {
call_notifier = 1;
- pm_qos_array[target]->target_value = extreme_value;
+ atomic_set(&pm_qos_array[target]->target_value, extreme_value);
pr_debug(KERN_ERR "new target for qos %d is %d\n", target,
- pm_qos_array[target]->target_value);
+ atomic_read(&pm_qos_array[target]->target_value));
}
spin_unlock_irqrestore(&pm_qos_lock, flags);

@@ -193,14 +193,7 @@
*/
int pm_qos_requirement(int pm_qos_class)
{
- int ret_val;
- unsigned long flags;
-
- spin_lock_irqsave(&pm_qos_lock, flags);
- ret_val = pm_qos_array[pm_qos_class]->target_value;
- spin_unlock_irqrestore(&pm_qos_lock, flags);
-
- return ret_val;
+ return atomic_read(&pm_qos_array[pm_qos_class]->target_value);
}
EXPORT_SYMBOL_GPL(pm_qos_requirement);


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