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

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Date:   Wed, 25 Oct 2023 17:38:46 +0800
From:   Zeng Heng <zengheng4@...wei.com>
To:     <broonie@...nel.org>, <joey.gouly@....com>, <will@...nel.org>,
        <amit.kachhap@....com>, <rafael@...nel.org>,
        <catalin.marinas@....com>, <james.morse@....com>,
        <mark.rutland@....com>, <maz@...nel.org>,
        <viresh.kumar@...aro.org>, <sumitg@...dia.com>,
        <yang@...amperecomputing.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <wangxiongfeng2@...wei.com>, <xiexiuqi@...wei.com>
Subject: [PATCH 2/3] cpufreq: CPPC: Keep the target core awake when reading its cpufreq rate

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.

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