Re: [PATCH] cpufreq: intel_pstate: Load when ACPI PCCH is present

Srinivas Pandruvada
2018-07-17T17:23:00Z

On Tue, 2018-07-17 at 18:13 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Currently, intel_pstate doesn't load if _PSS is not present on
> HP Proliant systems, because it expects the firmware to take over
> CPU performance scaling in that case. However, if ACPI PCCH is
> present, the firmware expects the kernel to use it for CPU
> performance scaling and the pcc-cpufreq driver is loaded for that.
>
> Unfortunately, the firmware interface used by that driver is not
> scalable for fundamental reasons, so pcc-cpufreq is way suboptimal
> on systems with more than just a few CPUs. In fact, it is better to
> avoid using it at all.
>
> For this reason, modify intel_pstate to look for ACPI PCCH if _PSS
> is not present and load if it is there.
>
> Fixes: fbbcdc0744da (intel_pstate: skip the driver if ACPI has power
> mgmt option)
> Reported-by: Andreas Herrmann <aherrmann@suse.com>
> Tested-by: Andreas Herrmann <aherrmann@suse.com>
> Reviewed-by: Andreas Herrmann <aherrmann@suse.com>
> Cc: 4.17+ <stable@vger.kernel.org> # 4.17+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

But do we need a change as done by the following commit in in pcc-
cpufreq.c?

"
commit 8a61e12e84597b5f8155ac91b44dea866ccfaac2
Author: Yinghai Lu <yinghai@kernel.org>
Date: Fri Sep 20 10:43:56 2013 -0700

acpi-cpufreq: skip loading acpi_cpufreq after intel_pstate

"

Thanks,
Srinivas

> ---
> drivers/cpufreq/intel_pstate.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -2391,6 +2391,18 @@ static bool __init intel_pstate_no_acpi_
> return true;
> }
>
> +static bool __init intel_pstate_no_acpi_pcch(void)
> +{
> + acpi_status status;
> + acpi_handle handle;
> +
> + status = acpi_get_handle(NULL, "\\_SB", &handle);
> + if (ACPI_FAILURE(status))
> + return true;
> +
> + return !acpi_has_method(handle, "PCCH");
> +}
> +
> static bool __init intel_pstate_has_acpi_ppc(void)
> {
> int i;
> @@ -2450,7 +2462,10 @@ static bool __init intel_pstate_platform
>
> switch (plat_info[idx].data) {
> case PSS:
> - return intel_pstate_no_acpi_pss();
> + if (!intel_pstate_no_acpi_pss())
> + return false;
> +
> + return intel_pstate_no_acpi_pcch();
> case PPC:
> return intel_pstate_has_acpi_ppc() && !force_load;
> }
>