linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Update EPP for AlderLake mobile

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Message-ID: <2e5cd069996b1abb477eb4e817391db6f9bfa097.camel@gmail.com>
Date:   Wed, 29 Dec 2021 12:22:28 +0200
From:   Artem Bityutskiy <dedekind1@...il.com>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        lenb@...nel.org, rafael@...nel.org, viresh.kumar@...aro.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: intel_pstate: Update EPP for AlderLake mobile

On Thu, 2021-12-16 at 10:33 -0800, Srinivas Pandruvada wrote:
> There is an expectation from users that they can get frequency specified
> by cpufreq/cpuinfo_max_freq when conditions permit. But with AlderLake
> mobile it may not be possible. This is possible that frequency is clipped
> based on the system power-up EPP value. In this case users can update
> cpufreq/energy_performance_preference to some performance oriented EPP to
> limit clipping of frequencies.
> 
> To get out of box behavior as the prior generations of CPUs, update EPP
> for AlderLake mobile CPUs on boot. On prior generations of CPUs EPP = 128
> was enough to get maximum frequency, but with AlderLake mobile the
> equivalent EPP is 102. Since EPP is model specific, this is possible that
> they have different meaning on each generation of CPU.
> 
> The current EPP string "balance_performance" corresponds to EPP = 128.
> Change the EPP corresponding to "balance_performance" to 102 for only
> AlderLake mobile CPUs and update this on each CPU during boot.
> 
> To implement reuse epp_values[] array and update the modified EPP at the
> index for BALANCE_PERFORMANCE. Add a dummy EPP_INDEX_DEFAULT to
> epp_values[] to match indexes in the energy_perf_strings[].
> 
> After HWP PM is enabled also update EPP when "balance_performance" is
> redefined for the very first time after the boot on each CPU. On
> subsequent suspend/resume or offline/online the old EPP is restored,
> so no specific action is needed.
> 
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>


I think this patch alone makes things a bit inconsistent, because the
'x86_energy_perf_policy' does not get adjusted.

Ideally, constants like HWP_EPP_BALANCE_PERFORMANCE should go away from
arch/x86/include/asm/msr-index.h, along with all users.

Artem.