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Message-ID: <ZT-tSoCYR-818pa3@e129154.nice.arm.com>
Date: Mon, 30 Oct 2023 14:19:06 +0100
From: Beata Michalska <beata.michalska@....com>
To: Sumit Gupta <sumitg@...dia.com>
Cc: Zeng Heng <zengheng4@...wei.com>, broonie@...nel.org,
joey.gouly@....com, will@...nel.org, amit.kachhap@....com,
rafael@...nel.org, catalin.marinas@....com, james.morse@....com,
maz@...nel.org, viresh.kumar@...aro.org,
yang@...amperecomputing.com, linux-kernel@...r.kernel.org,
linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
wangxiongfeng2@...wei.com, xiexiuqi@...wei.com,
Ionela Voinescu <ionela.voinescu@....com>,
linux-tegra <linux-tegra@...r.kernel.org>,
Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 2/3] cpufreq: CPPC: Keep the target core awake when
reading its cpufreq rate
On Wed, Oct 25, 2023 at 08:27:23PM +0530, Sumit Gupta wrote:
>
>
>
> > [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())?
>
>
> This patch seems mostly based on my previous patch [1] and discussed here
> [2] already. Beata [CCed] shared an alternate approach [3] leveraging
> existing code from 'topology.c' to get the average freq for last tick
> period.
>
>
> Beata,
>
> Could you share v2 of [3] with the request to merge. We can try to solve the
> issue with CPU IDLE case later on top?
>
Will do (same for the below request if feasible)
---
BR
B.
> Additionally, also please include the fix in [4] if it looks fine.
>
> Best Regards,
> Sumit Gupta
>
> [1] https://lore.kernel.org/all/20230418113459.12860-7-sumitg@nvidia.com/
> [2] https://lore.kernel.org/lkml/cde1d8a9-3a21-e82b-7895-40603a14d898@nvidia.com/T/#m2174305de4706006e0bd9c103a0e5ff61cea7a12
> [3]
> https://lore.kernel.org/lkml/20230606155754.245998-1-beata.michalska@arm.com/
> [4]
> https://lore.kernel.org/lkml/6a5710f6-bfbb-5dfd-11cd-0cd02220cee7@nvidia.com/
>
>
> > >
> > > Reported-by: Sumit Gupta <sumitg@...dia.com>
> > > Link: https://lore.kernel.org/all/20230418113459.12860-7-sumitg@nvidia.com/
> > > Signed-off-by: Zeng Heng <zengheng4@...wei.com>
> > > ---
> > > 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
> > >
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