Re: [PATCH 2/3] cpufreq: CPPC: Keep the target core awake when reading its cpufreq rate

[Zeng Heng]

在 2023/10/25 18:54, Mark Rutland 写道:
> [adding Ionela]
>
> On Wed, Oct 25, 2023 at 05:38:46PM +0800, 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 while cstate feature is enabled.
> IIUC there's a pretty deliberate split with all the actual reading of the AMU
> living in arch/arm64/kernel/topolgy.c, and the driver code being (relatively)
> generic.
>
> We already have code in arch/arm64/kernel/topolgy.c to read counters on a
> specific CPU; why can't e reuse that (and avoid exporting cpu_has_amu_feat())?
>
> Mark.

In this scenario, both topology.c and cppc_acpi.c do not provide an API 
to keep the AMU online

during the whole sampling period. Just using cpc_read_ffh at the start 
and end of the sampling

period is not enough.

However, I can propose cpc_ffh_supported() function to replace the 
cpu_has_amu_feat() as v2

if you think this patch set is still valuable.


Thanks,

Zeng Heng

> > Reported-by: Sumit Gupta <sumitg@xxxxxxxxxx>
> > Link: https://lore.kernel.org/all/20230418113459.12860-7-sumitg@xxxxxxxxxx/
> > Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
> > ---
> >   drivers/cpufreq/cppc_cpufreq.c | 39 ++++++++++++++++++++++++++--------
> >   1 file changed, 30 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> > index fe08ca419b3d..321a9dc9484d 100644
> > --- a/drivers/cpufreq/cppc_cpufreq.c
> > +++ b/drivers/cpufreq/cppc_cpufreq.c
> > @@ -90,6 +90,12 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
> >   				 struct cppc_perf_fb_ctrs *fb_ctrs_t0,
> >   				 struct cppc_perf_fb_ctrs *fb_ctrs_t1);
> >   
> > +struct fb_ctr_pair {
> > +	u32 cpu;
> > +	struct cppc_perf_fb_ctrs fb_ctrs_t0;
> > +	struct cppc_perf_fb_ctrs fb_ctrs_t1;
> > +};
> > +
> >   /**
> >    * cppc_scale_freq_workfn - CPPC arch_freq_scale updater for frequency invariance
> >    * @work: The work item.
> > @@ -840,9 +846,24 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
> >   	return (reference_perf * delta_delivered) / delta_reference;
> >   }
> >   
> > +static int cppc_get_perf_ctrs_pair(void *val)
> > +{
> > +	struct fb_ctr_pair *fb_ctrs = val;
> > +	int cpu = fb_ctrs->cpu;
> > +	int ret;
> > +
> > +	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs->fb_ctrs_t0);
> > +	if (ret)
> > +		return ret;
> > +
> > +	udelay(2); /* 2usec delay between sampling */
> > +
> > +	return cppc_get_perf_ctrs(cpu, &fb_ctrs->fb_ctrs_t1);
> > +}
> > +
> >   static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
> >   {
> > -	struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
> > +	struct fb_ctr_pair fb_ctrs = { .cpu = cpu, };
> >   	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
> >   	struct cppc_cpudata *cpu_data = policy->driver_data;
> >   	u64 delivered_perf;
> > @@ -850,18 +871,18 @@ 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 0;
> > -
> > -	udelay(2); /* 2usec delay between sampling */
> > +	if (cpu_has_amu_feat(cpu))
> > +		ret = smp_call_on_cpu(cpu, cppc_get_perf_ctrs_pair,
> > +				      &fb_ctrs, false);
> > +	else
> > +		ret = cppc_get_perf_ctrs_pair(&fb_ctrs);
> >   
> > -	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
> >   	if (ret)
> >   		return 0;
> >   
> > -	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_t0,
> > +					      &fb_ctrs.fb_ctrs_t1);
> >   
> >   	return cppc_cpufreq_perf_to_khz(cpu_data, delivered_perf);
> >   }
> > --
> > 2.25.1