Re: [PATCH V3] SKL intel_pstate update MSR values when changing governors

From: Srinivas Pandruvada
Date: Fri Nov 20 2015 - 19:16:55 EST

On 11/18/2015 02:58 PM, Alexandra Yates wrote:
When changing from powersave to performance governors
Intel_pstate fails to update the MSR values that reflect the
max_perf_pct to 100%. For instance in SKL reading rdmsr 0x774:

Governor MSR max_perf_pct
========= ======== ============
Powersave 80002808 100%
Powersave 80002008 80%
Performance 80002028 [error] 100%
Performance 80002828 [expected] 100%

The line label [error] shows the culprit. At this point the MSR
should reflect the max_perf_pct that is 100%, that corresponds
to MSR 80002828 as shown on the next line of the example. Which
is the maximum performance for the Performance governor.
Instead it holds back the MSR value previously set by the
Powersave, in this case 80002028.

This patch allows the system to print the correct MSR value
80002828 that corresponds to the 100% max_perf_pct when changing
from powersave to performance governors.

For more information on the MSR values for SKL please visit
ISDM under Managing HWP.

Signed-off-by: Alexandra Yates <alexandra.yates@xxxxxxxxxxxxxxx>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
drivers/cpufreq/intel_pstate.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 2e31d09..0eeb7da 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1242,6 +1242,8 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
policy->max >= policy->cpuinfo.max_freq) {
pr_debug("intel_pstate: set performance\n");
limits = &performance_limits;
+ if (hwp_active)
+ intel_pstate_hwp_set();
return 0;

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