lkml.org 
[lkml]   [2020]   [Jul]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] cpufreq: intel_pstate: Fix EPP setting via sysfs in active mode
Date
"Rafael J. Wysocki" <rjw@rjwysocki.net> writes:

> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Because intel_pstate_set_energy_pref_index() reads and writes the
> MSR_HWP_REQUEST register without using the cached value of it used by
> intel_pstate_hwp_boost_up() and intel_pstate_hwp_boost_down(), those
> functions may overwrite the value written by it and so the EPP value
> set via sysfs may be lost.
>
> To avoid that, make intel_pstate_set_energy_pref_index() take the
> cached value of MSR_HWP_REQUEST just like the other two routines
> mentioned above and update it with the new EPP value coming from
> user space in addition to updating the MSR.
>
> Note that the MSR itself still needs to be updated too in case
> hwp_boost is unset or the boosting mechanism is not active at the
> EPP change time.
>
> Fixes: e0efd5be63e8 ("cpufreq: intel_pstate: Add HWP boost utility and sched util hooks")
> Reported-by: Francisco Jerez <currojerez@riseup.net>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Reviewed-by: Francisco Jerez <currojerez@riseup.net>

> ---
>
> This patch is on top of https://patchwork.kernel.org/patch/11689347/
>
> ---
> drivers/cpufreq/intel_pstate.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -653,11 +653,12 @@ static int intel_pstate_set_energy_pref_
> epp = cpu_data->epp_default;
>
> if (boot_cpu_has(X86_FEATURE_HWP_EPP)) {
> - u64 value;
> -
> - ret = rdmsrl_on_cpu(cpu_data->cpu, MSR_HWP_REQUEST, &value);
> - if (ret)
> - return ret;
> + /*
> + * Use the cached HWP Request MSR value, because the register
> + * itself may be updated by intel_pstate_hwp_boost_up() or
> + * intel_pstate_hwp_boost_down() at any time.
> + */
> + u64 value = READ_ONCE(cpu_data->hwp_req_cached);
>
> value &= ~GENMASK_ULL(31, 24);
>
> @@ -667,6 +668,12 @@ static int intel_pstate_set_energy_pref_
> epp = epp_values[pref_index - 1];
>
> value |= (u64)epp << 24;
> + /*
> + * The only other updater of hwp_req_cached in the active mode,
> + * intel_pstate_hwp_set(), is called under the same lock as this
> + * function, so it cannot run in parallel with the update below.
> + */
> + WRITE_ONCE(cpu_data->hwp_req_cached, value);
> ret = wrmsrl_on_cpu(cpu_data->cpu, MSR_HWP_REQUEST, value);
> } else {
> if (epp == -EINVAL)
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2020-07-29 07:49    [W:0.027 / U:0.736 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site