On Tuesday, March 01, 2016 01:17:37 PM Thomas Renninger wrote:

On Saturday, February 27, 2016 12:15:47 AM Rafael J. Wysocki wrote:

quoted

On Friday, February 26, 2016 05:38:00 PM Thomas Renninger wrote:

quoted

The assumption that BIOSes never want to have this register being set to
full performance (zero) is wrong.

While wrongly overruling this BIOS setting and set it from performance
to normal did not hurt that much, because nobody really knew the effects
inside Intel processors.

But with Broadwell-EP processor (E5-2687W v4) the CPU will not enter turbo
modes if this value is not set to performance.

So switch logic to tell the user in a friendly way (info) that the CPU is
in performance mode and how to switch via userspace if this is not
intended.

But otherwise trust that the BIOS has set the correct value here and do
not
blindly overrule.

How this has been found: SLE11 had this patch, SLE12 it slipped through.
It took quite some time to nail down that this patch missing is the reason
for not entering turbo modes with this specific processor.

Signed-off-by: Thomas Renninger <trenn@suse.com>

--- a/arch/x86/kernel/cpu/intel.c	2016-02-26 17:19:55.731042972 +0100
+++ b/arch/x86/kernel/cpu/intel.c	2016-02-26 17:20:48.598020581 +0100

@@ -377,8 +377,12 @@ static void init_intel_energy_perf(struc

 	u64 epb;
 	
 	/*

-	 * Initialize MSR_IA32_ENERGY_PERF_BIAS if not already initialized.
-	 * (x86_energy_perf_policy(8) is available to change it at run-time.)
+	 * On server platforms energy bias typically is set to
+	 * performance on purpose.
+	 * On other platforms it may happen that MSR_IA32_ENERGY_PERF_BIAS
+	 * did not get initialized properly by BIOS.
+	 * Best is to to keep BIOS settings and give the user a hint whether
+	 * to change it via cpupower-set(8) userspace tool at runtime.

 	 */
 	
 	if (!cpu_has(c, X86_FEATURE_EPB))
 	
 		return;

@@ -387,10 +391,8 @@ static void init_intel_energy_perf(struc

 	if ((epb & 0xF) != ENERGY_PERF_BIAS_PERFORMANCE)
 	
 		return;

-	pr_warn_once("ENERGY_PERF_BIAS: Set to 'normal', was 

'performance'\n");

quoted

quoted

-	pr_warn_once("ENERGY_PERF_BIAS: View and update with
x86_energy_perf_policy(8)\n"); -	epb = (epb & ~0xF) |
ENERGY_PERF_BIAS_NORMAL;
-	wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
+	pr_info_once("ENERGY_PERF_BIAS is set to 'performance'\n");
+	pr_info_once("ENERGY_PERF_BIAS: Update with cpupower-set(8)\n");

This doesn't need to be cpupower-set IMO.

You mean why switch the message from:
x86_energy_perf_policy to cpupower-set
?

IMO x86_energy_perf_policy should not exist. It has been introduce before
cpupower set -b.
Having an extra tool/binary for this functionality is an unneeded packaging 
overhead for distros.
Also having more and more of such CPU specific tools is not userfriendly.
cpupower supports all power relevant features of your CPU and on all 
architectures (or at least it should). People should know this one better
than "x86_energy_perf_policy" and theoretically intuitively find it, even 
without a message.

So it would be nice to get the message fixed as well.

My point is that since "cpupower set -b" is not the only way to set this,
it doesn't seem appropriate to refer to it explicitly from a kernel message.

I actually don't think the second message is necessary at all.

Thanks,
Rafael