Messages in this thread | | | Subject | Re: [RFC PATCH v3 1/6] PM: Introduce em_pd_get_higher_freq() | From | Douglas Raillard <> | Date | Thu, 17 Oct 2019 12:09:37 +0100 |
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Hi Dietmar,
On 10/17/19 10:58 AM, Dietmar Eggemann wrote: > On 11/10/2019 15:44, Douglas RAILLARD wrote: > > [...] > >> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h >> index d249b88a4d5a..dd6a35f099ea 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; > > Maybe you could mention in the header that this is the place where the > algorithm could be tuned. (even though it doesn't offer any tuning > interface, which is a good thing).
I'm not sure what you mean, the patch "title" contains "em_pd_get_higher_freq()", should it also mention where exactly inside the function the margin logic is implemented ?
>> + 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. >> + */ > > Maybe add a WARN_ONCE(1, "foobar"); here to indicate this unlikely event > (CPUfreq and EM framwork out of sync)?
Will do.
> [...] >
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