cpufreq: amd-pstate: cpufreq: amd-pstate: reset MSR_AMD_PERF_CTL register at init

MSR_AMD_PERF_CTL is guaranteed to be 0 on a cold boot. However, on a
kexec boot, for instance, it may have a non-zero value (if the cpu was
in a non-P0 Pstate).  In such cases, the cores with non-P0 Pstates at
boot will never be pushed to P0, let alone boost frequencies.

Kexec is a common workflow for reboot on Linux and this creates a
regression in performance. Fix it by explicitly setting the
MSR_AMD_PERF_CTL to 0 during amd_pstate driver init.

Cc: All applicable <stable@vger.kernel.org>
Acked-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Tested-by: Wyes Karny <wyes.karny@amd.com>
Signed-off-by: Wyes Karny <wyes.karny@amd.com>
Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index ace7d50..d844c6f 100644 (file)
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -424,12 +424,22 @@ static void amd_pstate_boost_init(struct amd_cpudata *cpudata)
        amd_pstate_driver.boost_enabled = true;
 }
 
+static void amd_perf_ctl_reset(unsigned int cpu)
+{
+       wrmsrl_on_cpu(cpu, MSR_AMD_PERF_CTL, 0);
+}
+
 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;
 
+       /*
+        * Resetting PERF_CTL_MSR will put the CPU in P0 frequency,
+        * which is ideal for initialization process.
+        */
+       amd_perf_ctl_reset(policy->cpu);
        dev = get_cpu_device(policy->cpu);
        if (!dev)
                return -ENODEV;