[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <c6bda238-166e-4de6-b0c7-4bddfb8ef6f4@amd.com>
Date: Tue, 18 Jun 2024 16:24:22 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Aaron Rainbolt <arainbolt@...cus.org>, linux-acpi@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: rafael@...nel.org, lenb@...nel.org, mmikowski@...cus.org,
Perry.Yuan@....com
Subject: Re: [PATCH V2 RFC] acpi: Allow ignoring _OSC CPPC v2 bit via kernel
parameter
On 6/18/2024 15:25, Aaron Rainbolt wrote:
> acpi: Allow ignoring _OSC CPPC v2 bit via kernel parameter
>
> The _OSC is supposed to contain a bit indicating whether the hardware
> supports CPPC v2 or not. This bit is not always set, causing CPPC v2 to
> be considered absent. This results in severe single-core performance
> issues with the EEVDF scheduler on heterogenous-core Intel processors.
>
> To work around this, provide a new kernel parameter, "ignore_osc_cppc_bit",
> which may be used to ignore the _OSC CPPC v2 bit and act as if the bit was
> enabled. This allows CPPC to be properly detected even if not "enabled" by
> _OSC, allowing users with problematic hardware to obtain decent single-core
> performance.
>
> Signed-off-by: Aaron Rainbolt <arainbolt@...cus.org>
>
> ---
>
> V1 -> V2: Rewrite to work in cpc_supported_by_cpu.
>
> RFC: I have not yet tested this patch to ensure it functions properly,
> nor have I attempted to compile it against mainline. My system takes
> a couple of hours or so to build a kernel, and I'd like to submit this
> for feedback now and test once it's sent.
Thanks, this matches what I suggested, hopefully it works when you test it.
One comment below though.
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index b600df82669d..af2d8973ba3a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2063,6 +2063,12 @@
> could change it dynamically, usually by
> /sys/module/printk/parameters/ignore_loglevel.
>
> + ignore_osc_cppc_bit
> + Assume CPPC is present and ignore the CPPC v2 bit from
> + the ACPI _OSC method. This is useful for working
> + around buggy firmware where CPPC is supported, but
> + _OSC incorrectly reports it as being absent.
> +
> ignore_rlimit_data
> Ignore RLIMIT_DATA setting for data mappings,
> print warning at first misuse. Can be changed via
> diff --git a/arch/x86/kernel/acpi/cppc.c b/arch/x86/kernel/acpi/cppc.c
> index ff8f25faca3d..7346a25e68ce 100644
> --- a/arch/x86/kernel/acpi/cppc.c
> +++ b/arch/x86/kernel/acpi/cppc.c
> @@ -11,6 +11,14 @@
>
> /* Refer to drivers/acpi/cppc_acpi.c for the description of functions */
>
> +static bool ignore_osc_cppc_bit;
> +static int __init parse_ignore_osc_cppc_bit(char *arg)
> +{
> + ignore_osc_cppc_bit = true;
> + return 0;
> +}
> +early_param("ignore_osc_cppc_bit", parse_ignore_osc_cppc_bit);
> +
> bool cpc_supported_by_cpu(void)
> {
> switch (boot_cpu_data.x86_vendor) {
> @@ -24,6 +32,10 @@ bool cpc_supported_by_cpu(void)
> return true;
> return boot_cpu_has(X86_FEATURE_CPPC);
> }
> +
> + if (ignore_osc_cppc_bit) {
> + return true;
> + }
I think you should move this check before the switch statement.
The reason is that such a workaround could then apply to any CPU
vendors and models that are AMD or Hygon too.
> return false;
> }
>
Powered by blists - more mailing lists