[PATCH] powerpc: Warn about use of smt_snooze_delay

[Christophe Leroy]

Le 25/06/2020 à 12:03, Joel Stanley a écrit :
> It's not done anything for a long time. Save the percpu variable, and
> emit a warning to remind users to not expect it to do anything.

Why not just drop the file entirely  if it is useless ?

Christophe

> 
> Signed-off-by: Joel Stanley <joel at jms.id.au>
> ---
>   arch/powerpc/kernel/sysfs.c | 41 +++++++++++++------------------------
>   1 file changed, 14 insertions(+), 27 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
> index 571b3259697e..530ae92bc46d 100644
> --- a/arch/powerpc/kernel/sysfs.c
> +++ b/arch/powerpc/kernel/sysfs.c
> @@ -32,29 +32,25 @@
>   
>   static DEFINE_PER_CPU(struct cpu, cpu_devices);
>   
> -/*
> - * SMT snooze delay stuff, 64-bit only for now
> - */
> -
>   #ifdef CONFIG_PPC64
>   
> -/* Time in microseconds we delay before sleeping in the idle loop */
> -static DEFINE_PER_CPU(long, smt_snooze_delay) = { 100 };
> +/*
> + * Snooze delay has not been hooked up since 3fa8cad82b94 ("powerpc/pseries/cpuidle:
> + * smt-snooze-delay cleanup.") and has been broken even longer. As was foretold in
> + * 2014:
> + *
> + *  "ppc64_util currently utilises it. Once we fix ppc64_util, propose to clean
> + *  up the kernel code."
> + *
> + * At some point in the future this code should be removed.
> + */
>   
>   static ssize_t store_smt_snooze_delay(struct device *dev,
>   				      struct device_attribute *attr,
>   				      const char *buf,
>   				      size_t count)
>   {
> -	struct cpu *cpu = container_of(dev, struct cpu, dev);
> -	ssize_t ret;
> -	long snooze;
> -
> -	ret = sscanf(buf, "%ld", &snooze);
> -	if (ret != 1)
> -		return -EINVAL;
> -
> -	per_cpu(smt_snooze_delay, cpu->dev.id) = snooze;
> +	WARN_ON_ONCE("smt_snooze_delay sysfs file has no effect\n");
>   	return count;
>   }
>   
> @@ -62,9 +58,9 @@ static ssize_t show_smt_snooze_delay(struct device *dev,
>   				     struct device_attribute *attr,
>   				     char *buf)
>   {
> -	struct cpu *cpu = container_of(dev, struct cpu, dev);
> +	WARN_ON_ONCE("smt_snooze_delay sysfs file has no effect\n");
>   
> -	return sprintf(buf, "%ld\n", per_cpu(smt_snooze_delay, cpu->dev.id));
> +	return sprintf(buf, "100\n");
>   }
>   
>   static DEVICE_ATTR(smt_snooze_delay, 0644, show_smt_snooze_delay,
> @@ -72,16 +68,7 @@ static DEVICE_ATTR(smt_snooze_delay, 0644, show_smt_snooze_delay,
>   
>   static int __init setup_smt_snooze_delay(char *str)
>   {
> -	unsigned int cpu;
> -	long snooze;
> -
> -	if (!cpu_has_feature(CPU_FTR_SMT))
> -		return 1;
> -
> -	snooze = simple_strtol(str, NULL, 10);
> -	for_each_possible_cpu(cpu)
> -		per_cpu(smt_snooze_delay, cpu) = snooze;
> -
> +	WARN_ON_ONCE("smt-snooze-delay command line option has no effect\n");
>   	return 1;
>   }
>   __setup("smt-snooze-delay=", setup_smt_snooze_delay);
>