Messages in this thread | | | Date | Thu, 18 May 2023 09:44:48 +0800 | Subject | Re: [PATCH v2 1/2] cpufreq: CPPC: keep target core awake when reading its cpufreq rate | From | Zeng Heng <> |
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在 2023/5/17 23:03, Sumit Gupta 写道: > > > On 17/05/23 13:47, Pierre Gondois wrote: >> External email: Use caution opening links or attachments >> >> >> +Ionela, Sumit, Yang, >> >> Hello Zeng, >> >> I think solutions around related issues were suggested at: >> >> [1] >> https://lore.kernel.org/all/20230418113459.12860-7-sumitg@nvidia.com/ >> [2] >> https://lore.kernel.org/all/20230328193846.8757-1-yang@os.amperecomputing.com/ >> [3] https://lore.kernel.org/all/ZEl1Fms%2FJmdEZsVn@arm.com/ >> >> About this patch, it seems to mean that CPPC counters of CPUx are always >> accessed from CPUx, even when they are not AMUs. For instance CPPC >> counters could be memory mapped and accessible from any CPU. >> cpu_has_amu_feat() should allow to probe if a CPU uses AMUs or not, >> and [2] had an implementation using it. >> >> Another comment about PATCH 2/2 is that if the counters are accessed >> through FFH, arm64 version of cpc_read_ffh() is calling >> counters_read_on_cpu(), and a comment in counters_read_on_cpu() seems >> to specify the function must be called with interrupt enabled. >> >> I think the best solution so far was the one at [3], suggested by >> Ionela, >> but it doesn't seem to solve your issue. Indeed, it is not checked >> whether >> the counters are AMU counters and that they must be remotely read (to >> have the CPU awake), >> >> Regards, >> Pierre >> > > I think the solution in [1] is simple and solves all the three cases. > Also, it provides better accuracy between the set and get frequency as > compared to [3]. > > This can be merged and can later still be improved in Upstream. > > If OK, I can send new version by changing the patch to apply for all > ARM SoC's with AMU and not specific to Tegra. > > Thank you, > Sumit Gupta > I vote solution [1] and it should be applied to all ARM SoCs with AMU.
Zeng Heng
>> >> On 5/16/23 15:32, Zeng Heng wrote: >>> As ARM AMU's document says, all counters are subject to any changes >>> in clock frequency, including clock stopping caused by the WFI and WFE >>> instructions. >>> >>> Therefore, using smp_call_on_cpu() to trigger target CPU to >>> read self's AMU counters, which ensures the counters are working >>> properly during calculation. >>> >>> Signed-off-by: Zeng Heng <zengheng4@huawei.com> >>> --- >>> drivers/cpufreq/cppc_cpufreq.c | 30 +++++++++++++++++++----------- >>> 1 file changed, 19 insertions(+), 11 deletions(-) >>> >>> diff --git a/drivers/cpufreq/cppc_cpufreq.c >>> b/drivers/cpufreq/cppc_cpufreq.c >>> index 022e3555407c..910167f58bb3 100644 >>> --- a/drivers/cpufreq/cppc_cpufreq.c >>> +++ b/drivers/cpufreq/cppc_cpufreq.c >>> @@ -837,9 +837,24 @@ static int cppc_perf_from_fbctrs(struct >>> cppc_cpudata *cpu_data, >>> return (reference_perf * delta_delivered) / delta_reference; >>> } >>> >>> +static int cppc_get_perf_ctrs_smp(void *val) >>> +{ >>> + int cpu = smp_processor_id(); >>> + struct cppc_perf_fb_ctrs *fb_ctrs = val; >>> + int ret; >>> + >>> + ret = cppc_get_perf_ctrs(cpu, fb_ctrs); >>> + if (ret) >>> + return ret; >>> + >>> + udelay(2); /* 2usec delay between sampling */ >>> + >>> + return cppc_get_perf_ctrs(cpu, fb_ctrs + 1); >>> +} >>> + >>> static unsigned int cppc_cpufreq_get_rate(unsigned int cpu) >>> { >>> - struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0}; >>> + struct cppc_perf_fb_ctrs fb_ctrs[2] = {0}; >>> struct cpufreq_policy *policy = cpufreq_cpu_get(cpu); >>> struct cppc_cpudata *cpu_data = policy->driver_data; >>> u64 delivered_perf; >>> @@ -847,19 +862,12 @@ static unsigned int >>> cppc_cpufreq_get_rate(unsigned int cpu) >>> >>> cpufreq_cpu_put(policy); >>> >>> - ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0); >>> - if (ret) >>> - return ret; >>> - >>> - udelay(2); /* 2usec delay between sampling */ >>> - >>> - ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1); >>> + ret = smp_call_on_cpu(cpu, cppc_get_perf_ctrs_smp, fb_ctrs, 1); >>> if (ret) >>> return ret; >>> >>> - delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0, >>> - &fb_ctrs_t1); >>> - >>> + delivered_perf = cppc_perf_from_fbctrs(cpu_data, fb_ctrs, >>> + fb_ctrs + 1); >>> return cppc_cpufreq_perf_to_khz(cpu_data, delivered_perf); >>> } >>>
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