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SubjectRe: [PATCH] cpufreq: intel_pstate: Fix rounding of core_pct
On 11/06/2014 06:02 μμ, Doug Smythies wrote:
>
> On 2104.06.11 07:08 Stratos Karafotis wrote:
>> On 11/06/2014 04:41 μμ, Doug Smythies wrote:
>>
>> No.
>>
>> The intent was only ever to round properly the pseudo floating point result of the divide.
>> It was much more important (ugh, well 4 times more) when FRACBITS was still 6, which also got changed to 8 in a recent patch.
>>
>
> Are you sure?
>
> Yes.
>
>> This rounding was very recently added.
>> As far as I can understand, I don't see the meaning of this rounding, as is.
>> Even if FRAC_BITS was 6, I think it would have almost no improvement in
>> calculations.
>
> Note: I had not seen this e-mail when I wrote a few minutes ago:
>
> You may be correct.
> If Dirk agrees, I will re-analyse the entire driver for rounding effects soon.
> When FRACBITS was 6 there were subtle cases where the driver would get stuck, and not make a final pstate change, with the default PID gains.
> Other things have changed, and the analysis needs to be re-done.
>

Could you please elaborate a little bit more what we need these 2 lines below?

if ((rem << 1) >= int_tofp(sample->mperf))
core_pct += 1;

Because nothing is mentioned for them in commit's changelog.
Do we need to round core_pct or not?
Because if we try to round it, I think this patch should work.

Thanks,
Stratos


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