Messages in this thread | | | Subject | Re: [v2] cpufreq / CPPC: Add cpuinfo_cur_freq support for CPPC | From | George Cherian <> | Date | Wed, 20 Jun 2018 14:59:15 +0530 |
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Hi JC,
Thanks for the review.
On 06/20/2018 02:09 AM, Jayachandran C wrote: > Hi George, > > Few comments on your patch: > > On Fri, Jun 15, 2018 at 03:03:15AM -0700, George Cherian wrote: >> Per Section 8.4.7.1.3 of ACPI 6.2, The platform provides performance >> feedback via set of performance counters. To determine the actual >> performance level delivered over time, OSPM may read a set of >> performance counters from the Reference Performance Counter Register >> and the Delivered Performance Counter Register. >> >> OSPM calculates the delivered performance over a given time period by >> taking a beginning and ending snapshot of both the reference and >> delivered performance counters, and calculating: >> >> delivered_perf = reference_perf X (delta of delivered_perf counter / delta of reference_perf counter). >> >> Implement the above and hook this to the cpufreq->get method. >> >> Signed-off-by: George Cherian <george.cherian@cavium.com> >> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> >> --- >> drivers/cpufreq/cppc_cpufreq.c | 71 ++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 71 insertions(+) >> >> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c >> index 3464580..3fe7625 100644 >> --- a/drivers/cpufreq/cppc_cpufreq.c >> +++ b/drivers/cpufreq/cppc_cpufreq.c >> @@ -296,10 +296,81 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy) >> return ret; >> } >> >> +static int cppc_get_rate_from_fbctrs(struct cppc_cpudata *cpu, >> + struct cppc_perf_fb_ctrs fb_ctrs_t0, >> + struct cppc_perf_fb_ctrs fb_ctrs_t1) >> +{ >> + u64 delta_reference, delta_delivered; >> + u64 reference_perf, delivered_perf; >> + >> + reference_perf = fb_ctrs_t0.reference_perf; >> + if (fb_ctrs_t1.reference > fb_ctrs_t0.reference) { >> + delta_reference = fb_ctrs_t1.reference - fb_ctrs_t0.reference; >> + } else { >> + /* >> + * Counters would have wrapped-around >> + * We also need to find whether the low level fw >> + * maintains 32 bit or 64 bit counters, to calculate >> + * the correct delta. >> + */ >> + if (fb_ctrs_t0.reference > (~(u32)0)) >> + delta_reference = (~((u64)0) - fb_ctrs_t0.reference) + >> + fb_ctrs_t1.reference; >> + else >> + delta_reference = (~((u32)0) - fb_ctrs_t0.reference) + >> + fb_ctrs_t1.reference; >> + } >> + >> + if (fb_ctrs_t1.delivered > fb_ctrs_t0.delivered) { >> + delta_delivered = fb_ctrs_t1.delivered - fb_ctrs_t0.delivered; >> + } else { >> + /* >> + * Counters would have wrapped-around >> + * We also need to find whether the low level fw >> + * maintains 32 bit or 64 bit counters, to calculate >> + * the correct delta. >> + */ >> + if (fb_ctrs_t0.delivered > (~(u32)0)) >> + delta_delivered = (~((u64)0) - fb_ctrs_t0.delivered) + >> + fb_ctrs_t1.delivered; >> + else >> + delta_delivered = (~((u32)0) - fb_ctrs_t0.delivered) + >> + fb_ctrs_t1.delivered; >> + } > > Having this code repeated twice does not look great. Also the math here > is not correct, since (~0 - val2 + val1) is off by one. Because of > binary representation, unsigned subtraction will work even if > val2 < val1. So cleaner way would be to do: > > static inline u64 ts_sub(u64 t1, u64 t0) > { > if (t1 > t0 || t0 > ~(u32)0) > return t1 - t0; > > return (u32)t1 - (u32)t0; > } > > And then use ts_sub in both places above.
I was actually thinking to replace the whole comparison with a single line irrespective of rollover or not. It will look something like this.
delta = (u32)(((1UL << 32) - t0) + t1);
This will also take care of the value being off by one. > > JC. >
Regards, -George
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