[PATCH v4 02/13] cpufreq: amd-pstate: enable AMD Precision Boost mode switch

Perry Yuan
2022-07-15T10:05:40Z

Add support to switch AMD precision boost state to scale cpu max
frequency that will help to improve the processor throughput.

when set boost state to be enabled, user will need to execute below commands,
the CPU will reach absolute maximum performance level or the highest perf which
CPU physical support. This performance level may not be sustainable for
long durations, it will help to improve the IO workload tasks.

* turn on CPU boost state under root
echo 1 > /sys/devices/system/cpu/cpufreq/boost

If user set boost off,the CPU can reach to the maximum sustained
performance level of the process, that level is the process can maintain
continously working and definitely it can save some power compared to
boost on mode.

* turn off CPU boost state under root
echo 0 > /sys/devices/system/cpu/cpufreq/boost

Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
---
arch/x86/include/asm/msr-index.h | 2 ++
drivers/cpufreq/amd-pstate.c | 22 +++++++++++++++++++---
2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 869508de8269..b952fd6d6916 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -559,6 +559,8 @@
#define AMD_CPPC_MIN_PERF(x) (((x) & 0xff) << 8)
#define AMD_CPPC_DES_PERF(x) (((x) & 0xff) << 16)
#define AMD_CPPC_ENERGY_PERF_PREF(x) (((x) & 0xff) << 24)
+#define AMD_CPPC_PRECISION_BOOST_BIT 25
+#define AMD_CPPC_PRECISION_BOOST_ENABLED BIT_ULL(AMD_CPPC_PRECISION_BOOST_BIT)

/* AMD Performance Counter Global Status and Control MSRs */
#define MSR_AMD64_PERF_CNTR_GLOBAL_STATUS 0xc0000300
diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 9ac75c1cde9c..188e055e24a2 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -122,6 +122,7 @@ struct amd_cpudata {

u64 freq;
bool boost_supported;
+ u64 cppc_hw_conf_cached;
};

static inline int pstate_enable(bool enable)
@@ -438,18 +439,27 @@ static int amd_pstate_set_boost(struct cpufreq_policy *policy, int state)
{
struct amd_cpudata *cpudata = policy->driver_data;
int ret;
+ u64 value;

if (!cpudata->boost_supported) {
pr_err("Boost mode is not supported by this processor or SBIOS\n");
return -EINVAL;
}

- if (state)
+ ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_HW_CTL, &value);
+ if (ret)
+ return ret;
+
+ if (state) {
+ value |= AMD_CPPC_PRECISION_BOOST_ENABLED;
policy->cpuinfo.max_freq = cpudata->max_freq;
- else
+ } else {
+ value &= ~AMD_CPPC_PRECISION_BOOST_ENABLED;
policy->cpuinfo.max_freq = cpudata->nominal_freq;
-
+ }
policy->max = policy->cpuinfo.max_freq;
+ WRITE_ONCE(cpudata->cppc_hw_conf_cached, value);
+ wrmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_HW_CTL, value);

ret = freq_qos_update_request(&cpudata->req[1],
policy->cpuinfo.max_freq);
@@ -478,6 +488,7 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
struct device *dev;
struct amd_cpudata *cpudata;
+ u64 value;

dev = get_cpu_device(policy->cpu);
if (!dev)
@@ -542,6 +553,11 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)

policy->driver_data = cpudata;

+ ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_HW_CTL, &value);
+ if (ret)
+ return ret;
+ WRITE_ONCE(cpudata->cppc_hw_conf_cached, value);
+
amd_pstate_boost_init(cpudata);

return 0;
--
2.32.0