linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Fix cpuinfo_cur

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Date:   Tue, 25 Jul 2017 23:46:34 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Huaisheng HS1 Ye <yehs1@...ovo.com>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        NingTing Cheng <chengnt@...ovo.com>
Subject: Re: [PATCH] cpufreq: intel_pstate: Fix cpuinfo_cur_freq after performance governor changes

On Tuesday, July 25, 2017 07:03:36 AM Huaisheng HS1 Ye wrote:
> Hi Srinivas,
> Your idea is great, but your patch at cpufreq.c will force all platforms to use scaling_cur_freq as first choice when userspace wants to access cpuinfo_cur_freq. It is ok for intel x86 platfrom but hard to say with other platforms.
> I modified it like that, it looks more reasonable. How about that?
> 
> Hi Rafael,
> Deleting "get" function pointer within intel_pstate would lead to sysfs
> interface cpuinfo_cur_freq disappearing, because of
> cpufreq_add_dev_interface will check "cpufreq_driver->get" for it.

Which is exactly what I want.

cpuinfo_cur_freq is bogus for intel_pstate and it should have never been
exported for this driver.

> Perhaps just return 0 with in intel_pstate_get would be a workaround for this
> issue, how about it?
> 
> I have tested this patch based on Purley platform, both Hardware and Software
> P-states works correct, we could get accurate and same frequency from
> cpuinfo_cur_freq and scaling_cur_freq.

But this is not correct.  These two attributes should not be expected to always
return the same value.

Thanks,
Rafael