linux-kernel - Re: [Patch v5 2/2] ACPI: processor: reduce CPUFREQ thermal reduction pctg for Tegra241

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Date:   Mon, 23 Oct 2023 09:53:20 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Sumit Gupta <sumitg@...dia.com>
Cc:     <rafael@...nel.org>, <rui.zhang@...el.com>, <lenb@...nel.org>,
        <linux-acpi@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <treding@...dia.com>,
        <jonathanh@...dia.com>, <bbasu@...dia.com>, <sanjayc@...dia.com>,
        <ksitaraman@...dia.com>, <srikars@...dia.com>, <jbrasen@...dia.com>
Subject: Re: [Patch v5 2/2] ACPI: processor: reduce CPUFREQ thermal reduction
 pctg for Tegra241

On Sat, Oct 14, 2023 at 04:24:26PM +0530, Sumit Gupta wrote:
> From: Srikar Srimath Tirumala <srikars@...dia.com>
>
> Current implementation of processor_thermal performs software throttling
> in fixed steps of "20%" which can be too coarse for some platforms.
> We observed some performance gain after reducing the throttle percentage.
> Change the CPUFREQ thermal reduction percentage and maximum thermal steps
> to be configurable. Also, update the default values of both for Nvidia
> Tegra241 (Grace) SoC. The thermal reduction percentage is reduced to "5%"
> and accordingly the maximum number of thermal steps are increased as they
> are derived from the reduction percentage.
>
> Signed-off-by: Srikar Srimath Tirumala <srikars@...dia.com>
> Co-developed-by: Sumit Gupta <sumitg@...dia.com>
> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
> ---
>  drivers/acpi/arm64/Makefile          |  1 +
>  drivers/acpi/arm64/thermal_cpufreq.c | 20 ++++++++++++++++
>  drivers/acpi/processor_thermal.c     | 35 +++++++++++++++++++++++++---
>  include/linux/acpi.h                 |  9 +++++++
>  4 files changed, 62 insertions(+), 3 deletions(-)
>  create mode 100644 drivers/acpi/arm64/thermal_cpufreq.c
>
> diff --git a/drivers/acpi/arm64/Makefile b/drivers/acpi/arm64/Makefile
> index 143debc1ba4a..3f181d8156cc 100644
> --- a/drivers/acpi/arm64/Makefile
> +++ b/drivers/acpi/arm64/Makefile
> @@ -5,3 +5,4 @@ obj-$(CONFIG_ACPI_GTDT) 	+= gtdt.o
>  obj-$(CONFIG_ACPI_APMT) 	+= apmt.o
>  obj-$(CONFIG_ARM_AMBA)		+= amba.o
>  obj-y				+= dma.o init.o
> +obj-$(CONFIG_ACPI)		+= thermal_cpufreq.o

Do we really need CONFIG_ACPI here ? We won't be building this if it
is not enabled.

If this is for some module building, then does it make sense to have
more specific config ? May be CONFIG_ACPI_THERMAL ?

> diff --git a/drivers/acpi/arm64/thermal_cpufreq.c b/drivers/acpi/arm64/thermal_cpufreq.c
> new file mode 100644
> index 000000000000..de834fb013e7
> --- /dev/null
> +++ b/drivers/acpi/arm64/thermal_cpufreq.c
> @@ -0,0 +1,20 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <linux/acpi.h>
> +
> +#ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
> +#define SMCCC_SOC_ID_T241      0x036b0241
> +
> +int acpi_thermal_cpufreq_pctg(void)
> +{
> +	s32 soc_id = arm_smccc_get_soc_id_version();
> +
> +	/*
> +	 * Check JEP106 code for NVIDIA Tegra241 chip (036b:0241) and
> +	 * reduce the CPUFREQ Thermal reduction percentage to 5%.
> +	 */
> +	if (soc_id == SMCCC_SOC_ID_T241)
> +		return 5;
> +
> +	return 0;
> +}
> +#endif

Since this looks like arch specific hook/callback, not sure if it is good
idea to have "arch_" in the function name. But if Rafael is OK with the name
I am fine with this as well.

--
Regards,
Sudeep