linux-kernel - Re: [PATCH v3] hwmon: coretemp: avoid RDMSR interruptions to isolated CPUs

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Message-ID: <20221228155937.GA64676@roeck-us.net>
Date:   Wed, 28 Dec 2022 07:59:37 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Fenghua Yu <fenghua.yu@...el.com>, linux-kernel@...r.kernel.org,
        linux-hwmon@...r.kernel.org,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v3] hwmon: coretemp: avoid RDMSR interruptions to
 isolated CPUs

On Fri, Dec 16, 2022 at 05:24:08PM -0300, Marcelo Tosatti wrote:
> The coretemp driver uses rdmsr_on_cpu calls to read
> MSR_IA32_PACKAGE_THERM_STATUS/MSR_IA32_THERM_STATUS registers,
> which contain information about current core temperature.
> 
> For certain low latency applications, the RDMSR interruption exceeds
> the applications requirements.
> 
> So do not create core files in sysfs, for CPUs which have
> isolation and nohz_full enabled.
> 
> Temperature information from the housekeeping cores should be
> sufficient to infer die temperature.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>

Applied to hwmon-next.

Thanks,
Guenter

> ---
> v3: do not create sysfs files for isolated CPUs (Guenter Roeck)
> v2: improve changelog to mention that an error is returned,
>      and sysfs file is not disabled (Guenter Roeck)
> 
> diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
> index 9bee4d33fbdf..619dfde7a712 100644
> --- a/drivers/hwmon/coretemp.c
> +++ b/drivers/hwmon/coretemp.c
> @@ -27,6 +27,7 @@
>  #include <asm/msr.h>
>  #include <asm/processor.h>
>  #include <asm/cpu_device_id.h>
> +#include <linux/sched/isolation.h>
>  
>  #define DRVNAME	"coretemp"
>  
> @@ -458,6 +459,9 @@ static int create_core_data(struct platform_device *pdev, unsigned int cpu,
>  	u32 eax, edx;
>  	int err, index, attr_no;
>  
> +	if (!housekeeping_cpu(cpu, HK_TYPE_MISC))
> +		return 0;
> +
>  	/*
>  	 * Find attr number for sysfs:
>  	 * We map the attr number to core id of the CPU