On Wed, Jun 13, 2012 at 3:14 PM, Vincent Guittot
[off-list ref] wrote:

On 13 June 2012 10:59, Jean Pihet [off-list ref] wrote:

quoted

Vincent,

On Tue, Jun 12, 2012 at 2:02 PM, Vincent Guittot
[off-list ref] wrote:

quoted

Use cpu compatibility field and clock-frequency field of DT to
estimate the capacity of each core of the system

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
?arch/arm/kernel/topology.c | ?122 ++++++++++++++++++++++++++++++++++++++++++++
?1 file changed, 122 insertions(+)

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index 2f85a64..0c2aee4 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c

@@ -17,6 +17,7 @@

?#include <linux/percpu.h>
?#include <linux/node.h>
?#include <linux/nodemask.h>
+#include <linux/of.h>
?#include <linux/sched.h>

?#include <asm/cputype.h>

@@ -47,6 +48,122 @@ void set_power_scale(unsigned int cpu, unsigned long power)

? ? ? ?per_cpu(cpu_scale, cpu) = power;
?}

+#ifdef CONFIG_OF
+struct cpu_efficiency {
+ ? ? ? const char *compatible;
+ ? ? ? unsigned long efficiency;
+};
+
+/*
+ * Table of relative efficiency of each processors
+ * The efficiency value must fit in 20bit. The final
+ * cpu_scale value must be in the range [1:2048[.

Typo here.

I realize that I have use absolute value instead of SCHED_POWER_SCALE.
The cpu_scale value must be in the range 0 < cpu_scale < 2*SCHED_POWER_SCALE

quoted

quoted

+ * Processors that are not defined in the table,
+ * use the default SCHED_POWER_SCALE value for cpu_scale.
+ */
+struct cpu_efficiency table_efficiency[] = {
+ ? ? ? {"arm,cortex-a15", 3891},
+ ? ? ? {"arm,cortex-a7", ?2048},

How are those results measured or computed? Is this purely related to
the number crunching performance?

These values are based on ARM's figures which say that Cortex-A15 is
1,9 faster than Cortex-A7 at same frequency. So the inputs are ARM's
figures. Then, the absolute values are arbitrary with the constraint
of being large enough for precision and small enough to make the
computation in an unsigned long

quoted

Also more generally what if the cores frequencies are changing?

Up to now, the scheduler takes into account the maximum capacity of a
core when it checks the load balance of the system.

Jean,

Various discussions around power-aware scheduling have amplified the
need for the scheduler to have some knowledge of DVFS. This would then
require the scheduler to track 'cpu_power' ( = max power) and perhaps
a new variable 'current_power' that is changed by the DVFS framework.

The first goal, though, is to make sure that the scheduler can handle
different cpu_power values due to asymmetric cores.

/Amit