Hi Patrick,
On 5/16/19 1:42 PM, Patrick Bellasi wrote:
On 08-May 18:42, [email protected] wrote:
From: Douglas RAILLARD <[email protected]>
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.
It's worth to add a small description and definition of what we mean by
"OPP efficiency". Despite being just an RFC, it could help to better
understand what we are after.
Right, here efficiency=capacity/power.
[...]
+/** + * 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, as a per-1024
value.
^^^^^^^^
here...
+ *
+ * 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) / 1024;
^^^^
... end here we should probably better use SCHED_CAPACITY_SCALE
instead of hard-coding in values, isn't it?
"cs->cost*cost_margin/1024" is not a capacity, it's a cost as defined here:
https://elixir.bootlin.com/linux/latest/source/include/linux/energy_model.h#L17
Actually, it's in milliwatts, but it's not better the better way to look at
it to understand it IMHO.
The margin is expressed as a "per-1024" value just like we use percents'
in everyday life, so it has no unit. If we want to avoid hard-coded values
here, I can introduce an ENERGY_COST_MARGIN_SCALE macro.
+ break;
+ }
+ }
+
[...]
Best,
Patrick
Thanks,
Douglas
