Messages in this thread | | | Date | Wed, 6 Jun 2018 17:20:00 +0200 | From | Juri Lelli <> | Subject | Re: [RFC PATCH v3 03/10] PM: Introduce an Energy Model management framework |
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On 06/06/18 15:37, Quentin Perret wrote: > Hi Dietmar, > > On Wednesday 06 Jun 2018 at 15:12:15 (+0200), Dietmar Eggemann wrote: > > > +static void fd_update_cs_table(struct em_cs_table *cs_table, int cpu) > > > +{ > > > + unsigned long cmax = arch_scale_cpu_capacity(NULL, cpu); > > > + int max_cap_state = cs_table->nr_cap_states - 1; > > > + unsigned long fmax = cs_table->state[max_cap_state].frequency; > > > + int i; > > > + > > > + for (i = 0; i < cs_table->nr_cap_states; i++) > > > + cs_table->state[i].capacity = cmax * > > > + cs_table->state[i].frequency / fmax; > > > +} > > > > This has issues on a 32bit system. cs_table->state[i].capacity (unsigned > > long) overflows with the frequency values stored in Hz. > > Ah, thank you very much for pointing this out ! I haven't tried on a 32bit > machine yet, my bad. I'll fix that for v4. > > > > > Maybe something like this to cure it: > > > > diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c > > index 6ad53f1cf7e6..c13b3eb8bf35 100644 > > --- a/kernel/power/energy_model.c > > +++ b/kernel/power/energy_model.c > > @@ -144,9 +144,11 @@ static void fd_update_cs_table(struct em_cs_table *cs_table, int cpu) > > unsigned long fmax = cs_table->state[max_cap_state].frequency; > > int i; > > > > - for (i = 0; i < cs_table->nr_cap_states; i++) > > - cs_table->state[i].capacity = cmax * > > - cs_table->state[i].frequency / fmax; > > + for (i = 0; i < cs_table->nr_cap_states; i++) { > > + u64 val = (u64)cmax * cs_table->state[i].frequency; > > + do_div(val, fmax); > > + cs_table->state[i].capacity = (unsigned long)val; > > + } > > } > > Hmmm yes, that should work. > > > > > This brings me to another question. Let's say there are multiple users of > > the Energy Model in the system. Shouldn't the units of frequency and power > > not standardized, maybe Mhz and mW? > > The task scheduler doesn't care since it is only interested in power diffs > > but other user might do. > > So the good thing about specifying units is that we can probably assume > ranges on the values. If the power is in mW, assuming that we're talking > about a single CPU, it'll probably fit in 16 bits. 65W/core should be > a reasonable upper-bound ? > But there are also vendors who might not be happy with disclosing absolute > values ... These are sometimes considered sensitive and only relative > numbers are discussed publicly. Now, you can also argue that we already > have units specified in IPA for ex, and that it doesn't really matter if > a driver "lies" about the real value, as long as the ratios are correct. > And I guess that anyone can do measurement on the hardware and get those > values anyway. So specifying a unit (mW) for the power is probably a > good idea.
Mmm, I remember we fought quite a bit while getting capacity-dmpis-mhz binding accepted, and one of the musts was that the values were going to be normalized. So, normalized power values again maybe?
Best,
- Juri
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