linux-kernel - Re: [PATCH v2 30/45] arm_mpam: resctrl: Pre-allocate assignable monitors

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Message-ID: <20260106142937.00000e33@huawei.com>
Date: Tue, 6 Jan 2026 14:29:37 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Ben Horgan <ben.horgan@....com>
CC: <amitsinght@...vell.com>, <baisheng.gao@...soc.com>,
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Subject: Re: [PATCH v2 30/45] arm_mpam: resctrl: Pre-allocate assignable
 monitors

On Fri, 19 Dec 2025 18:11:32 +0000
Ben Horgan <ben.horgan@....com> wrote:

> From: James Morse <james.morse@....com>
> 
> When there are not enough monitors, MPAM is able to emulate ABMC by making
> a smaller number of monitors assignable. These monitors still need to be
> allocated from the driver, and mapped to whichever control/monitor group
> resctrl wants to use them with.
> 
> Add a second array to hold the monitor values indexed by resctrl's cntr_id.
> 
> When CDP is in use, two monitors are needed so the available number of
> counters halves. Platforms with one monitor will have zero monitors when
> CDP is in use.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Signed-off-by: Ben Horgan <ben.horgan@....com>
> ---
> Changes since rfc:
> Move __free
> kmalloc -> kcalloc
>  

Trivial comments only,
Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

>  static inline int mpam_alloc_csu_mon(struct mpam_class *class)
> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
> index bea16bc096f7..e96d320c219c 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c

> +/*
> + * This must run after all event counters have been picked so that any free
> + * running counters have already been allocated.
> + */
> +static int mpam_resctrl_monitor_init_abmc(struct mpam_resctrl_mon *mon)
> +{
> +	struct mpam_resctrl_res *res = &mpam_resctrl_controls[RDT_RESOURCE_L3];
> +	struct rdt_resource *l3 = &res->resctrl_res;
> +	struct mpam_class *class = mon->class;
> +	u16 num_mbwu_mon;
> +
> +	if (mon->mbwu_idx_to_mon) {
> +		pr_debug("monitors free running\n");
> +		return 0;
> +	}
> +
> +	int *rmid_array __free(kfree) =
> +		kcalloc(resctrl_arch_system_num_rmid_idx(), sizeof(int), GFP_KERNEL);

It's a long line, but I'd prefer sizeof(*rmid_array).
could use kmalloc_array to avoid zeroing just before you fill it with -1.

> +
> +	if (!rmid_array) {
> +		pr_debug("Failed to allocate RMID array\n");
> +		return -ENOMEM;
> +	}
> +	memset(rmid_array, -1, resctrl_arch_system_num_rmid_idx() * sizeof(int));
> +
> +	num_mbwu_mon = class->props.num_mbwu_mon;
> +	mon->assigned_counters = __alloc_mbwu_array(mon->class, num_mbwu_mon);
> +	if (IS_ERR(mon->assigned_counters))
> +		return PTR_ERR(mon->assigned_counters);
> +	mon->mbwu_idx_to_mon = no_free_ptr(rmid_array);
> +
> +	mpam_resctrl_monitor_sync_abmc_vals(l3);
> +
> +	return 0;
> +}