Re: [PATCH 2/2 V7] intel_pstate: add kernel parameter to force loading on Sun X86 servers.

From: ethan zhao
Date: Thu Dec 04 2014 - 22:39:08 EST


On 2014/12/5 7:03, Linda Knippers wrote:
On 12/4/2014 5:38 PM, Kristen Carlson Accardi wrote:
On Thu, 04 Dec 2014 23:10:58 +0100
"Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx> wrote:

On Thursday, December 04, 2014 11:07:31 AM Ethan Zhao wrote:
To force loading on Oracle Sun X86 servers, provide one kernel command line

intel_pstate = ora_force
I would suggest to change the name of the option to "oracle_force" or "sun_force"
for clarity.

Anyway, I need an ACK from Kristen if this patch is to be applied.

For those who be aware of the risk of no power capping capabily working and
try to get better performance with this driver.

Signed-off-by: Ethan Zhao <ethan.zhao@xxxxxxxxxx>
v2: change to hardware vendor specific naming parameter.
v4: refine code and doc.
v5&v6: fix a typo in doc.
v7: change enum PCC to PPC.

Documentation/kernel-parameters.txt | 5 +++++
drivers/cpufreq/intel_pstate.c | 6 +++++-
2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 479f332..7d0983e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1446,6 +1446,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
Do not enable intel_pstate as the default
scaling driver for the supported processors
+ ora_force
+ Force loading intel_pstate on Oracle Sun Servers(X86).
+ only for those who be aware of the risk of no power capping
+ capability working and try to get better performance with this
+ driver.
That is not sufficiently clear. What does "risk of no power capping capability
working" mean, in particular?

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 1bb62ca..2654e13 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -866,6 +866,7 @@ static struct cpufreq_driver intel_pstate_driver = {
static int __initdata no_load;
+static unsigned int ora_force;
static int intel_pstate_msrs_not_valid(void)
@@ -1003,7 +1004,8 @@ static bool intel_pstate_platform_pwr_mgmt_exists(void)
case PSS:
return intel_pstate_no_acpi_pss();
case PPC:
- return intel_pstate_has_acpi_ppc();
+ return intel_pstate_has_acpi_ppc() &&
+ (!ora_force);
@@ -1078,6 +1080,8 @@ static int __init intel_pstate_setup(char *str)
if (!strcmp(str, "disable"))
no_load = 1;
+ if (!strcmp(str, "ora_force"))
+ ora_force = 1;
return 0;
early_param("intel_pstate", intel_pstate_setup);
And can anyone please remind me what was wrong with a "force" option that would
work for everyone, not just Oracle/Sun?

That was my suggestion as well (i.e. a parameter to bypass the vendor
checks), but Linda didn't like it. My personal opinion is that unless
it's generic, I don't really feel like having a force option solely for
oracle. I'm not convinced you want this for production machines, and I
think for debug purposes I don't want a vendor specific param.
I'd be happy with it if it somehow disabled what the platform is doing,
but it doesn't. I don't see the point of forcing intel_pstate if you
can't force the platform to stop doing power management at the same time.
Even if it's for test/debug purposes, I'm not sure what you're testing
when you have dueling power management.
Most of the power management functions is done by SP(service processor) on Sun X86
servers, the 'force' parameter is not supposed to disable whole platform working I think,
with intel_pstate, it doesn't do CPU power capping issued via _PPC notification. but all
other rest parts of the power management still work. There is no scene as HP proliant OS
mode that OS could control everything(sorry, I don't know Proliant Architecture).

So at least, it doesn't make sense to Oracle Sun X86 servers, provide an OS option to stop
all PM functions even disable ACPI at all.

If the users could be aware of that the power capping doesn't work with CPUs. they could
load intel_pstate driver, though there may be faulty in SP . they still could monitor and
manage the power consumption of other parts in the server.

Perhaps this is what we would test/have tested with intel_pstate.

There is a public manual about PM command in Sun server SP may could help you to understand
the difference.

The description would need to be different too since I think on
ProLiant, power capping can happen at any time, even if the
system is in OS control mode and the intel_pstate driver is
Does that mean only the CPU power capping not work ? If so, they work the same way.

Can anyone suggest a description for a force option that would
make sense generically?
the 'force' option means CPU power capping (frequency limited) not work to all,
right ?


-- ljk

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