[PATCH] acpi: Allow ignoring _OSC CPPC v2 bit via kernel parameter

Aaron Rainbolt
2024-06-18T02:54:20Z

acpi: Allow ignoring _OSC CPPC v2 bit via kernel parameter

The _OSC is supposed to contain a bit indicating whether the hardware
supports CPPC v2 or not. This bit is not always set, causing CPPC v2 to
be considered absent. This results in severe single-core performance
issues with the EEVDF scheduler.

To work around this, provide a new kernel parameter,
"processor.ignore_osc_cppc_bit", which may be used to ignore the _OSC
CPPC v2 bit and act as if the bit was enabled. This allows CPPC to be
properly detected even if not "enabled" by _OSC, allowing users with
problematic hardware to obtain decent single-core performance.

Tested-by: Michael Mikowski <mmikowski@kfocus.org>
Signed-off-by: Aaron Rainbolt <arainbolt@kfocus.org>

---

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 1d857978f5f4..53406dd6cb87 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -671,7 +671,7 @@ static inline void arch_init_invariance_cppc(void) { }
*
* Return: 0 for success or negative value for err.
*/
-int acpi_cppc_processor_probe(struct acpi_processor *pr)
+int acpi_cppc_processor_probe(struct acpi_processor *pr, bool ignore_osc_cppc_bit)
{
struct acpi_buffer output = {ACPI_ALLOCATE_BUFFER, NULL};
union acpi_object *out_obj, *cpc_obj;
@@ -686,7 +686,7 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)

if (!osc_sb_cppc2_support_acked) {
pr_debug("CPPC v2 _OSC not acked\n");
- if (!cpc_supported_by_cpu()) {
+ if (!ignore_osc_cppc_bit && !cpc_supported_by_cpu()) {
pr_debug("CPPC is not supported by the CPU\n");
return -ENODEV;
}
diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
index 67db60eda370..a183bca6c1c5 100644
--- a/drivers/acpi/processor_driver.c
+++ b/drivers/acpi/processor_driver.c
@@ -33,6 +33,11 @@ MODULE_AUTHOR("Paul Diefenbaugh");
MODULE_DESCRIPTION("ACPI Processor Driver");
MODULE_LICENSE("GPL");

+static bool ignore_osc_cppc_bit = false;
+module_param(ignore_osc_cppc_bit, bool, 0);
+MODULE_PARM_DESC(ignore_osc_cppc_bit,
+ "Ignore _OSC CPPC bit, assume CPPC v2 is present");
+
static int acpi_processor_start(struct device *dev);
static int acpi_processor_stop(struct device *dev);

@@ -170,7 +175,7 @@ static int __acpi_processor_start(struct acpi_device *device)
if (pr->flags.need_hotplug_init)
return 0;

- result = acpi_cppc_processor_probe(pr);
+ result = acpi_cppc_processor_probe(pr, ignore_osc_cppc_bit);
if (result && !IS_ENABLED(CONFIG_ACPI_CPU_FREQ_PSS))
dev_dbg(&device->dev, "CPPC data invalid or not present\n");

diff --git a/include/acpi/processor.h b/include/acpi/processor.h
index 3f34ebb27525..79fd61b3f537 100644
--- a/include/acpi/processor.h
+++ b/include/acpi/processor.h
@@ -358,10 +358,10 @@ int acpi_map_cpuid(phys_cpuid_t phys_id, u32 acpi_id);
int acpi_get_cpuid(acpi_handle, int type, u32 acpi_id);

#ifdef CONFIG_ACPI_CPPC_LIB
-extern int acpi_cppc_processor_probe(struct acpi_processor *pr);
+extern int acpi_cppc_processor_probe(struct acpi_processor *pr, bool ignore_osc_cppc_bit);
extern void acpi_cppc_processor_exit(struct acpi_processor *pr);
#else
-static inline int acpi_cppc_processor_probe(struct acpi_processor *pr)
+static inline int acpi_cppc_processor_probe(struct acpi_processor *pr, bool ignore_osc_cppc_bit)
{
return 0;
}