ACPI: processor: perflib: Avoid updating frequency QoS unnecessarily

Modify acpi_processor_get_platform_limit() to avoid updating its
frequency QoS request when the _PPC return value has not changed
by comparing that value to the previous _PPC return value stored in
the performance_platform_limit field of the struct acpi_processor
corresponding to the given CPU.

While at it, do the _PPC return value check against the state count
earlier, to avoid setting performance_platform_limit to an invalid
value, and make acpi_processor_ppc_init() use FREQ_QOS_MAX_DEFAULT_VALUE
as the "no limit" frequency QoS for consistency.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c
index 0da85fc..4265814 100644 (file)
--- a/drivers/acpi/processor_perflib.c
+++ b/drivers/acpi/processor_perflib.c
@@ -76,13 +76,16 @@ static int acpi_processor_get_platform_limit(struct acpi_processor *pr)
 
        index = ppc;
 
+       if (pr->performance_platform_limit == index ||
+           ppc >= pr->performance->state_count)
+               return 0;
+
        pr_debug("CPU %d: _PPC is %d - frequency %s limited\n", pr->id,
                 index, index ? "is" : "is not");
 
        pr->performance_platform_limit = index;
 
-       if (ppc >= pr->performance->state_count ||
-           unlikely(!freq_qos_request_active(&pr->perflib_req)))
+       if (unlikely(!freq_qos_request_active(&pr->perflib_req)))
                return 0;
 
        /*
@@ -178,9 +181,16 @@ void acpi_processor_ppc_init(struct cpufreq_policy *policy)
                if (!pr)
                        continue;
 
+               /*
+                * Reset performance_platform_limit in case there is a stale
+                * value in it, so as to make it match the "no limit" QoS value
+                * below.
+                */
+               pr->performance_platform_limit = 0;
+
                ret = freq_qos_add_request(&policy->constraints,
-                                          &pr->perflib_req,
-                                          FREQ_QOS_MAX, INT_MAX);
+                                          &pr->perflib_req, FREQ_QOS_MAX,
+                                          FREQ_QOS_MAX_DEFAULT_VALUE);
                if (ret < 0)
                        pr_err("Failed to add freq constraint for CPU%d (%d)\n",
                               cpu, ret);