Messages in this thread | | | Subject | Re: [PATCH v2] cpufreq / CPPC: Add cpuinfo_cur_freq support for CPPC | From | George Cherian <> | Date | Wed, 20 Jun 2018 14:47:02 +0530 |
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Hi Prakash,
Thanks for the review.
On 06/19/2018 01:51 AM, Prakash, Prashanth wrote: > External Email > > Hi George, > > On 6/15/2018 4:03 AM, 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 { > There should be another if () here to check if the reference counters are equal. > We cannot assume, there was a overflow when the counters are equal. As I > mentioned on last patch, the counters *may* pause in idle states. My Bad... I somehow, over looked that point. In case of delta_reference being zero there is actually a check below to avoid divide-by-zero. There I returned reference perf instead of desired perf, same I will take care in v3. Isn't that sufficient or is there a need for an explicit check here for delta = zero?
Moreover the delta calculation am planning to replace with single line comparison in v3 for both normal and overflow case. >> + /* >> + * 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; >> + } >> + >> + if (delta_reference) /* Check to avoid divide-by zero */ >> + delivered_perf = (reference_perf * delta_delivered) / >> + delta_reference; >> + else >> + delivered_perf = reference_perf; > > If we cannot compute delivered performance then we should return > desired/requested perf and not reference_perf. > Noted!! >> + >> + return cppc_cpufreq_perf_to_khz(cpu, delivered_perf); >> +} >> + >> +static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum) >> +{ >> + struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0}; >> + struct cppc_cpudata *cpu = all_cpu_data[cpunum]; >> + int ret; >> + >> + ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t0); >> + if (ret) >> + return ret; >> + >> + udelay(2); /* 2usec delay between sampling */ >> + >> + ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t1); >> + if (ret) >> + return ret; >> + >> + return cppc_get_rate_from_fbctrs(cpu, fb_ctrs_t0, fb_ctrs_t1); >> +} >> + >> static struct cpufreq_driver cppc_cpufreq_driver = { >> .flags = CPUFREQ_CONST_LOOPS, >> .verify = cppc_verify_policy, >> .target = cppc_cpufreq_set_target, >> + .get = cppc_cpufreq_get_rate, >> .init = cppc_cpufreq_cpu_init, >> .stop_cpu = cppc_cpufreq_stop_cpu, >> .name = "cppc_cpufreq", > > Thanks, > Prashanth >
Thanks, -George
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