Re: [PATCH 2/2] cpufreq: intel_pstate: Fix set_policy interface for no_turbo

On Wed, Jun 8, 2016 at 2:48 AM, Srinivas Pandruvada
[off-list ref] wrote:

On Wed, 2016-06-08 at 02:42 +0200, Rafael J. Wysocki wrote:

quoted

On Wed, Jun 8, 2016 at 2:38 AM, Srinivas Pandruvada
[off-list ref] wrote:

quoted

When turbo is disabled, the set_policy interface is broken.
For example, when turbo is disabled and
cpuinfo.max = 2900000 (full max turbo frequency)
Setting the limits results in frequency less than settings:
Set 1000000 KHz results in 0700000 KHz
Set 1500000 KHz results in 1100000 KHz
Set 2000000 KHz results in  1500000 KHz

This is because limits->max_perf fraction is calculated using max
turbo frequency as the reference, but when the max P-State is
capped in the function intel_pstate_get_min_max, the reference
is not the max turbo P-State. This results in reducing max
P-State.

One option is to always use max turbo as reference for calculating
limits. But this will not be correct. By definition the
intel_pstate
sysfs limits, shows percentage of available performance. So when
BIOS has disabled turbo, the available performance is max non
turbo.
So the max_perf_pct should still show 100%.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel
.com>

I guess we need this in -stable?

Yes.

quoted

If so, all of them, or is there a specific starting point?

I think this is from (even in 3.10, it should have the same behavior
looking at the code).

OK

All applicable, then?