Re: [PATCH v9 26/31] fs,x86/resctrl: Compute number of RMIDs as minimum across resources

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Tony,

On 8/29/25 12:33 PM, Tony Luck wrote:
> resctrl assumes that only the L3 resource supports monitor events, so
> it simply takes the rdt_resource::num_rmid from RDT_RESOURCE_L3 as
> the system's number of RMIDs.
> 
> The addition of telemetry events in a different resource breaks that
> assumption.
> 
> Compute the number of available RMIDs as the minimum value across
> all mon_capable resources (analogous to how the number of CLOSIDs
> is computed across alloc_capable resources).
> 
> Note that mount time enumeration of the telemetry resource means that
> this number can be reduced. If this happens, then some memory will
> be wasted as the allocations for rdt_l3_mon_domain::states[] will be

Same comment as v8. :(

> larger than needed.
> 
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---
>  arch/x86/kernel/cpu/resctrl/core.c | 15 +++++++++++++--
>  fs/resctrl/rdtgroup.c              |  5 +++++
>  2 files changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index dbad8d301e03..8aa7d9105971 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -110,12 +110,23 @@ struct rdt_hw_resource rdt_resources_all[RDT_NUM_RESOURCES] = {
>  	},
>  };
>  
> +/**
> + * resctrl_arch_system_num_rmid_idx - Compute number of supported RMIDs
> + *				      (minimum across all mon_capable resource)
> + *
> + * Return: Number of supported RMIDs at time of call. Note that mount time
> + * enumeration of resources may reduce the number.
> + */
>  u32 resctrl_arch_system_num_rmid_idx(void)
>  {
> -	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> +	u32 num_rmids = U32_MAX;
> +	struct rdt_resource *r;
> +
> +	for_each_mon_capable_rdt_resource(r)
> +		num_rmids = min(num_rmids, r->num_rmid);
>  
>  	/* RMID are independent numbers for x86. num_rmid_idx == num_rmid */
> -	return r->num_rmid;
> +	return num_rmids == U32_MAX ? 0 : num_rmids;
>  }
>  
>  struct rdt_resource *resctrl_arch_get_resource(enum resctrl_res_level l)
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index 01e42130e98b..3201e9cad8da 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -4116,6 +4116,11 @@ void resctrl_offline_mon_domain(struct rdt_resource *r, struct rdt_domain_hdr *h
>   * During boot this may be called before global allocations have been made by
>   * resctrl_l3_mon_resource_init().
>   *
> + * This routine is called at resctrl init time. The number of supported RMIDs

Regarding "This routine is called at resctrl init time.":
domain_setup_l3_mon_state() is called during CPU online that can occur *any* time
after resctrl init, including after resctrl mount.

How about "Called during CPU online that may run as soon as CPU online
callbacks are set up during resctrl initialization."? (Or use "CPU hot plug notifiers
are registered", whatever terms you decide to use consistently.)

> + * may be reduced if additional mon_capable resources are enumerated at mount
> + * time. This means the rdt_l3_mon_domain::mbm_states[] and
> + * rdt_l3_mon_domain::rmid_busy_llc allocations may be larger than needed.
> + *
>   * Returns 0 for success, or -ENOMEM.
>   */
>  static int domain_setup_l3_mon_state(struct rdt_resource *r, struct rdt_l3_mon_domain *d)

Reinette