On 01/30/2014 04:31 PM, Peter Zijlstra wrote:
On Thu, Jan 30, 2014 at 03:09:22PM +0100, Daniel Lezcano wrote:
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 90aef084..130debf 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -654,6 +654,9 @@ struct rq {
#endif
struct sched_avg avg;
+#ifdef CONFIG_CPU_IDLE
+ int idle_index;
+#endif
};
So my 'problem' with this is that I've no ff'ing clue what the
idle_index is and what I can do with it.
The cpuidle framework works with index corresponding to the index in the
idle states array. This array contains all the idle states the backend
driver supports. The cpuidle framework will ask for the governor what
idle state it should uses for the cpu, the governor will look at the
different characteristics of the idle states + timing information and
returns an index corresponding to the idle state the governor thinks
suit better. This step is the 'cpuidle_select'.
Then the cpuidle framework calls the idle callback associated with the
idle state at the index location. The cpu will stay blocked on this
callback until an interrupt occurs. This step is the 'cpuidle_enter'.
Between the 'cpuidle_select' and 'cpuidle_enter', this patch stores the
current idle state the cpu is about to enter (it stores the index). So
from the scheduler and the current cpuidle api it is easy to get
information about the idle state a cpu is:
struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
struct cpuidle_state *state = &drv->states[rq->index];
And from the state, we have the following informations:
struct cpuidle_state {
[ ... ]
unsigned int exit_latency; /* in US */
int power_usage; /* in mW */
unsigned int target_residency; /* in US */
bool disabled; /* disabled on all CPUs */
[ ... ]
};
IIRC, Alex Shi sent a patchset to improve the choosing of the idlest cpu
and the exit_latency was needed.
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