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

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Message-ID: <564FB7EE.6030507@linux.intel.com>
Date:	Fri, 20 Nov 2015 16:16:46 -0800
From:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:	Alexandra Yates <alexandra.yates@...ux.intel.com>, lenb@...nel.org,
	viresh.kumar@...aro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, rjw@...ysocki.net
Subject: Re: [PATCH V3] SKL intel_pstate update MSR values when changing governors



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@...ux.intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> ---
>   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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