linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Drop ->get from intel

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Thu, 27 Jul 2017 09:17:49 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Huaisheng HS1 Ye <yehs1@...ovo.com>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: intel_pstate: Drop ->get from intel_pstate
 structure

On 26-07-17, 00:42, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The ->get callback in the intel_pstate structure was mostly there
> for the scaling_cur_freq sysfs attribute to work, but after commit
> f8475cef9008 (x86: use common aperfmperf_khz_on_cpu() to calculate
> KHz using APERF/MPERF) that attribute uses arch_freq_get_on_cpu()
> provided by the x86 arch code on all processors supported by
> intel_pstate, so it doesn't need the ->get callback from the
> driver any more.
> 
> Moreover, the very presence of the ->get callback in the intel_pstate
> structure causes the cpuinfo_cur_freq attribute to be present when
> intel_pstate operates in the active mode, which is bogus, because
> the role of that attribute is to return the current CPU frequency
> as seen by the hardware.  For intel_pstate, though, this is just an
> average frequency and not really current, but computed for the
> previous sampling interval (the actual current frequency may be
> way different at the point this value is obtained by reading from
> cpuinfo_cur_freq), and after commit 82b4e03e01bc (intel_pstate: skip
> scheduler hook when in "performance" mode) the value in
> cpuinfo_cur_freq may be stale or just 0, depending on the driver's
> operation mode.  In fact, however, on the hardware supported by
> intel_pstate there is no way to read the current CPU frequency
> from it, so the cpuinfo_cur_freq attribute should not be present
> at all when this driver is in use.
> 
> For this reason, drop intel_pstate_get() and clear the ->get
> callback pointer pointing to it, so that the cpuinfo_cur_freq is
> not present for intel_pstate in the active mode any more.
> 
> Fixes: 82b4e03e01bc (intel_pstate: skip scheduler hook when in "performance" mode)
> Reported-by: Huaisheng Ye <yehs1@...ovo.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpufreq/intel_pstate.c |    8 --------
>  1 file changed, 8 deletions(-)
> 
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -1674,13 +1674,6 @@ static int intel_pstate_init_cpu(unsigne
>  	return 0;
>  }
>  
> -static unsigned int intel_pstate_get(unsigned int cpu_num)
> -{
> -	struct cpudata *cpu = all_cpu_data[cpu_num];
> -
> -	return cpu ? get_avg_frequency(cpu) : 0;
> -}
> -
>  static void intel_pstate_set_update_util_hook(unsigned int cpu_num)
>  {
>  	struct cpudata *cpu = all_cpu_data[cpu_num];
> @@ -1921,7 +1914,6 @@ static struct cpufreq_driver intel_pstat
>  	.setpolicy	= intel_pstate_set_policy,
>  	.suspend	= intel_pstate_hwp_save_state,
>  	.resume		= intel_pstate_resume,
> -	.get		= intel_pstate_get,
>  	.init		= intel_pstate_cpu_init,
>  	.exit		= intel_pstate_cpu_exit,
>  	.stop_cpu	= intel_pstate_stop_cpu,

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh