em_pd_get_higher_freq() returns a frequency greater or equal to the
provided one while taking into account a given cost margin. It also
skips inefficient OPPs that have a higher cost than another one with a
higher frequency.
The efficiency of an OPP is measured as efficiency=capacity/power.
OPPs with the same efficiency are assumed to be equivalent, since they
will consume as much energy for a given amount of work to do. That may
take more or less time depending on the frequency, but will consume the
same energy.
Signed-off-by: Douglas RAILLARD <douglas.raill...@arm.com>
---
include/linux/energy_model.h | 53 ++++++++++++++++++++++++++++++++++++
1 file changed, 53 insertions(+)
diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
index aa027f7bcb3e..cc9819967f8d 100644
--- a/include/linux/energy_model.h
+++ b/include/linux/energy_model.h
@@ -159,6 +159,53 @@ static inline int em_pd_nr_cap_states(struct
em_perf_domain *pd)
return pd->nr_cap_states;
}
+#define EM_COST_MARGIN_SCALE 1024U
+
+/**
+ * em_pd_get_higher_freq() - Get the highest frequency that does not exceed the
+ * given cost margin compared to min_freq
+ * @pd : performance domain for which this must be done
+ * @min_freq : minimum frequency to return
+ * @cost_margin : allowed margin compared to min_freq, on the
+ * EM_COST_MARGIN_SCALE scale.
+ *
+ * Return: the chosen frequency, guaranteed to be at least as high as min_freq.
+ */
+static inline unsigned long em_pd_get_higher_freq(struct em_perf_domain *pd,
+ unsigned long min_freq, unsigned long cost_margin)
+{
+ unsigned long max_cost = 0;
+ struct em_cap_state *cs;
+ int i;
+
+ if (!pd)
+ return min_freq;
+
+ /* Compute the maximum allowed cost */
+ for (i = 0; i < pd->nr_cap_states; i++) {
+ cs = &pd->table[i];
+ if (cs->frequency >= min_freq) {
+ max_cost = cs->cost +
+ (cs->cost * cost_margin) / EM_COST_MARGIN_SCALE;
+ break;
+ }
+ }
+
+ /* Find the highest frequency that will not exceed the cost margin */
+ for (i = pd->nr_cap_states-1; i >= 0; i--) {
+ cs = &pd->table[i];
+ if (cs->cost <= max_cost)
+ return cs->frequency;
+ }
+
+ /*
+ * We should normally never reach here, unless min_freq was higher than
+ * the highest available frequency, which is not expected to happen.
+ */
+ return min_freq;
+}
+
+
#else
struct em_perf_domain {};
struct em_data_callback {};
@@ -182,6 +229,12 @@ static inline int em_pd_nr_cap_states(struct
em_perf_domain *pd)
{
return 0;
}
+
+static inline unsigned long em_pd_get_higher_freq(struct em_perf_domain *pd,
+ unsigned long min_freq, unsigned long cost_margin)
+{
+ return min_freq;
+}
#endif
#endif
--
2.22.0
