linux-kernel - Re: [PATCH v2 22/29] arm_mpam: Add helpers to allocate monitors

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Message-ID: <20250912141123.000068e2@huawei.com>
Date: Fri, 12 Sep 2025 14:11:23 +0100
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: James Morse <james.morse@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-acpi@...r.kernel.org>, D Scott Phillips OS
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 Deacon" <will@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Danilo Krummrich <dakr@...nel.org>, Ben Horgan <ben.horgan@....com>
Subject: Re: [PATCH v2 22/29] arm_mpam: Add helpers to allocate monitors

On Wed, 10 Sep 2025 20:43:02 +0000
James Morse <james.morse@....com> wrote:

> MPAM's MSC support a number of monitors, each of which supports
> bandwidth counters, or cache-storage-utilisation counters. To use
> a counter, a monitor needs to be configured. Add helpers to allocate
> and free CSU or MBWU monitors.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Ben Horgan <ben.horgan@....com>

One minor requested change inline that will probably otherwise get picked
up by someone's cleanup script

Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

> ---
>  drivers/resctrl/mpam_devices.c  |  2 ++
>  drivers/resctrl/mpam_internal.h | 35 +++++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index f536ebbcf94e..cf190f896de1 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -340,6 +340,8 @@ mpam_class_alloc(u8 level_idx, enum mpam_class_types type)
>  	class->level = level_idx;
>  	class->type = type;
>  	INIT_LIST_HEAD_RCU(&class->classes_list);
> +	ida_init(&class->ida_csu_mon);
> +	ida_init(&class->ida_mbwu_mon);
>  
>  	list_add_rcu(&class->classes_list, &mpam_classes);
>  
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 326ba9114d70..81c4c2bfea3d 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -210,6 +210,9 @@ struct mpam_class {
>  	/* member of mpam_classes */
>  	struct list_head	classes_list;
>  
> +	struct ida		ida_csu_mon;
> +	struct ida		ida_mbwu_mon;
> +
>  	struct mpam_garbage	garbage;
>  };
>  
> @@ -288,6 +291,38 @@ struct mpam_msc_ris {
>  	struct mpam_garbage	garbage;
>  };
>  
> +static inline int mpam_alloc_csu_mon(struct mpam_class *class)
> +{
> +	struct mpam_props *cprops = &class->props;
> +
> +	if (!mpam_has_feature(mpam_feat_msmon_csu, cprops))
> +		return -EOPNOTSUPP;
> +
> +	return ida_alloc_range(&class->ida_csu_mon, 0, cprops->num_csu_mon - 1,
> +			       GFP_KERNEL);
> +}
> +
> +static inline void mpam_free_csu_mon(struct mpam_class *class, int csu_mon)
> +{
> +	ida_free(&class->ida_csu_mon, csu_mon);
> +}
> +
> +static inline int mpam_alloc_mbwu_mon(struct mpam_class *class)
> +{
> +	struct mpam_props *cprops = &class->props;
> +
> +	if (!mpam_has_feature(mpam_feat_msmon_mbwu, cprops))
> +		return -EOPNOTSUPP;
> +
> +	return ida_alloc_range(&class->ida_mbwu_mon, 0,
> +			       cprops->num_mbwu_mon - 1, GFP_KERNEL);

ida_alloc_max() - which is just a wrapper that sets the minimum to 0
but none the less perhaps conveys things slightly better.

> +}
> +
> +static inline void mpam_free_mbwu_mon(struct mpam_class *class, int mbwu_mon)
> +{
> +	ida_free(&class->ida_mbwu_mon, mbwu_mon);
> +}
> +
>  /* List of all classes - protected by srcu*/
>  extern struct srcu_struct mpam_srcu;
>  extern struct list_head mpam_classes;