Re: [PATCH 3/3] intel_pstate: add module and kernel command line parameter to ignore ACPI _PPC

From: ethan zhao
Date: Sun Nov 23 2014 - 20:56:55 EST


On 2014/11/21 13:00, Linda Knippers wrote:

On 11/20/2014 10:07 PM, Ethan Zhao wrote:
Whatever I would like there is a way to load intel_pstate and give
it a try even it does not support all the PM features.
I think 'force' is OK.
Do you like it ? if the 'intel_pstate=force' would force the driver
to be loaded on to HP too ?
I'd prefer that it didn't. If you force the intel_pstate driver when
the platform thinks it's doing power management, then the OS and the
firmware are trying to manage the power at the same time. That's a
mess. If you want that for testing or debugging, what are you actually
testing or debugging? On an Oracle box, the firmware wouldn't stop
doing whatever it's doing just because the intel_pstate driver is
loaded, would it?
Yes, the platform wouldn't stop doing PM and the SCI even the intel_pstate
was loaded.
That option just give someone a chance who said "whatever I like intel_pstate
On Oracle Servers"

I also wonder what it means to "force" the intel_pstate driver
on systems with processors that aren't supported by the intel_pstate
driver. It wouldn't really be forced, would it?
Yes, wouldn't, such as AMD cpu-id and some old intel CPUs released before SandyBridge.
So the best way to to do the 'force' should be specific enough for "Oracle Sun server"


-- ljk


On Fri, Nov 21, 2014 at 5:23 AM, Kristen Carlson Accardi
<kristen@xxxxxxxxxxxxxxx> wrote:
On Thu, 20 Nov 2014 08:57:34 +0800
ethan <ethan.kernel@xxxxxxxxx> wrote:

å 2014å11æ20æï03:05ïKristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx> åéï

On Tue, 18 Nov 2014 17:37:06 +0900
Ethan Zhao <ethan.zhao@xxxxxxxxxx> wrote:

Add kernel command line parameter
intel_pstate = ignore_acpi_ppc
and module parameter
ignore_acpi_ppc = 1
to allow driver to ignore the ACPI _PPC existence even for Sun x86 servers.
These parameter could be used for debug\test\workaround etc purpose.

Signed-off-by: Ethan Zhao <ethan.zhao@xxxxxxxxxx>
What if we used a more generic parameter like "force" that would bypass
any vendor specific checks and just load anyway? This way we don't have
to add new parameters everything some new thing shows up that we want to

To be honest, I prefer more generic parameter. But to avoid the possible negative affect
To another vendors. I back to this way.
Well, your parameter can still impact other vendors as it is. it
is pretty typical to assume that using a parameter like "force" means
you know what you are doing and accept the risks. Especially if its
documented as such.

Documentation/kernel-parameters.txt | 3 +++
drivers/cpufreq/intel_pstate.c | 8 +++++++-
2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4c81a86..f502b85 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1446,6 +1446,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
Do not enable intel_pstate as the default
scaling driver for the supported processors
+ ignore_acpi_ppc
+ Ignore the existence of ACPI method _PPC for Sun x86 servers
+ and load the driver.

intremap= [X86-64, Intel-IOMMU]
on enable Interrupt Remapping (default)
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 7c5faea..388387b 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -870,6 +870,7 @@ static struct cpufreq_driver intel_pstate_driver = {

static int __initdata no_load;
+static unsigned int ignore_acpi_ppc;

static int intel_pstate_msrs_not_valid(void)
@@ -990,7 +991,7 @@ static bool intel_pstate_platform_pwr_mgmt_exists(void)
return true;
if (!strncmp(hdr.oem_id, v_info->oem_id, ACPI_OEM_ID_SIZE) &&
- intel_pstate_has_acpi_ppc())
+ intel_pstate_has_acpi_ppc() && !ignore_acpi_ppc)
return true;

@@ -1066,11 +1067,16 @@ static int __init intel_pstate_setup(char *str)

if (!strcmp(str, "disable"))
no_load = 1;
+ if (!strcmp(str, "ignore_acpi_ppc"))
+ ignore_acpi_ppc = 1;
return 0;
early_param("intel_pstate", intel_pstate_setup);

+module_param(ignore_acpi_ppc, uint, 0644);
+ "value 0 or non-zero. non-zero -> ignore ACPI _PPC and load this driver");
MODULE_AUTHOR("Dirk Brandewie <dirk.j.brandewie@xxxxxxxxx>");
MODULE_DESCRIPTION("'intel_pstate' - P state driver Intel Core processors");
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