On Wed, Jun 13, 2012 at 3:14 PM, Vincent Guittot vincent.guittot@linaro.org wrote:
On 13 June 2012 10:59, Jean Pihet jean.pihet@newoldbits.com wrote:
Vincent,
On Tue, Jun 12, 2012 at 2:02 PM, Vincent Guittot vincent.guittot@linaro.org wrote:
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
- 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
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