Re: [PATCH v6 15/23] virt/steal_monitor: Add control knobs for handling steal values

[Shrikanth Hegde <sshegde@linux.ibm.com>]

On 7/1/26 7:46 PM, Shrikanth Hegde wrote:
> These are the knobs to control the steal_monitor.
> 
> interval_ms:
> How often steal monitor checks for steal time.
> (Default: 1000 i.e 1 second)
> 
> This controls how fast steal monitor driver reacts to changes to
> the contention of physical CPUs. Since it does fair amount of
> work, setting too low will have overheads. If set to 0, on next
> work it will be set to default.

I will move to module_param_cb instead to do this.
This will address the WARN_ON issue as reported by sashiko.

> 
> low_threshold:
> lower threshold value in percentage * 100.
> (Default: 200, i.e 2% steal is considered as low threshold)
> 
> This determines what values should be considered as nil/no steal values.
> When steal monitor see steal time is below or equal to this value, it
> will increase the preferred CPUs by 1 core. Having value as zero
> might cause too much oscillations.
> 
> high_threshold:
> higher threshold value in percentage * 100
> (Default: 500, i.e 5% steal is considered as high threshold)
> 
> This determines what values should be considered as high steal values.
> When steal monitor sees steal time is higher than this value, it will
> reduce the preferred CPUs by 1 core.
> 

module_param_cb for these also will impose.

1. low cannot be greater than high
2. high cannot be lower than low.
3. high cannot be greater than 9999 (i.e 100% steal time)


> Also available at: Documentation/driver-api/steal-monitor.rst
> 
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>   drivers/virt/steal_monitor/sm_core.c | 18 +++++++++++++++++-
>   1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/virt/steal_monitor/sm_core.c b/drivers/virt/steal_monitor/sm_core.c
> index 92d5a0e3d8bf..1ba638224abb 100644
> --- a/drivers/virt/steal_monitor/sm_core.c
> +++ b/drivers/virt/steal_monitor/sm_core.c
> @@ -14,7 +14,23 @@
>   
>   #include "sm_core.h"
>   
> -struct steal_monitor sm_core_ctx;
> +struct steal_monitor sm_core_ctx = {
> +	.interval_ms = 1000,	/* 1 second */
> +	.high_threshold = 500,	/* 5% */
> +	.low_threshold = 200,	/* 2% */
> +};
> +
> +module_param_named(interval_ms, sm_core_ctx.interval_ms, uint, 0644);
> +MODULE_PARM_DESC(interval_ms,
> +		 "Sampling frequency for steal values in milliseconds (default: 1000)");
> +
> +module_param_named(high_threshold, sm_core_ctx.high_threshold, uint, 0644);
> +MODULE_PARM_DESC(high_threshold,
> +		 "High steal threshold (default: 500 i.e 5%)");
> +
> +module_param_named(low_threshold, sm_core_ctx.low_threshold, uint, 0644);
> +MODULE_PARM_DESC(low_threshold,
> +		 "Low steal threshold (default: 200 i.e 2%)");
>   
>   static int __init steal_monitor_init(void)
>   {