Re: [PATCH v12 09/26] x86/resctrl: Introduce interface to display number of monitoring counters

Reinette Chatre
2025-04-11T21:01:31Z

Hi Babu,

On 4/3/25 5:18 PM, Babu Moger wrote:
> The mbm_cntr_assign mode provides an option to the user to assign a
> counter to an RMID, event pair and monitor the bandwidth as long as
> the counter is assigned. Number of assignments depend on number of
> monitoring counters available.
>
> Provide the interface to display the number of monitoring counters

An interface can also be a function. To help make this work obvious
it can be specific:

Create 'num_mbm_cntrs' resctrl file that displays the number of
monitoring counters supported in each domain. 'num_mbm_cntrs'
is only visible to user space when the system supports
mbm_cntr_assign mode.

> supported in each domain. The resctrl file 'num_mbm_cntrs' is visible
> to user space when the system supports mbm_cntr_assign mode.
>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
...

> ---
> Documentation/arch/x86/resctrl.rst | 11 ++++++++++
> arch/x86/kernel/cpu/resctrl/monitor.c | 3 +++
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 30 ++++++++++++++++++++++++++
> 3 files changed, 44 insertions(+)
>
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index bb96b44019fe..35d908befdfb 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -284,6 +284,17 @@ with the following files:
> misleading values or display "Unavailable" if no counter is assigned
> to the event.
>
> +"num_mbm_cntrs":
> + The maximum number of monitoring counters (total of available and assigned
> + counters) in each domain when the system supports mbm_cntr_assign mode.
> +
> + For example, on a system with maximum of 32 memory bandwidth monitoring
> + counters in each of its L3 domains:
> + ::
> +
> + # cat /sys/fs/resctrl/info/L3_MON/num_mbm_cntrs
> + 0=32;1=32
> +
> "max_threshold_occupancy":
> Read/write file provides the largest value (in
> bytes) at which a previously used LLC_occupancy
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 6ed7e51d3fdb..028b49878ad0 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -1234,6 +1234,9 @@ int __init resctrl_mon_resource_init(void)
> else if (resctrl_arch_is_mbm_total_enabled())
> mba_mbps_default_event = QOS_L3_MBM_TOTAL_EVENT_ID;
>
> + if (r->mon.mbm_cntr_assignable)
> + resctrl_file_fflags_init("num_mbm_cntrs", RFTYPE_MON_INFO);

Missing RFTYPE_RES_CACHE?

> +
> return 0;
> }
>
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 626be6becca7..0c9d7a702b93 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -912,6 +912,30 @@ static int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
> return 0;
> }
>
> +static int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
> + struct seq_file *s, void *v)
> +{
> + struct rdt_resource *r = of->kn->parent->priv;
> + struct rdt_mon_domain *dom;
> + bool sep = false;
> +
> + cpus_read_lock();
> + mutex_lock(&rdtgroup_mutex);
> +
> + list_for_each_entry(dom, &r->mon_domains, hdr.list) {
> + if (sep)
> + seq_puts(s, ";");

seq_putc() can be used.

> +
> + seq_printf(s, "%d=%d", dom->hdr.id, r->mon.num_mbm_cntrs);
> + sep = true;
> + }
> + seq_puts(s, "\n");

seq_putc() can be used.

> +
> + mutex_unlock(&rdtgroup_mutex);
> + cpus_read_unlock();
> + return 0;
> +}
> +
> #ifdef CONFIG_PROC_CPU_RESCTRL
>
> /*
> @@ -1945,6 +1969,12 @@ static struct rftype res_common_files[] = {
> .seq_show = resctrl_mbm_assign_mode_show,
> .fflags = RFTYPE_MON_INFO,
> },
> + {
> + .name = "num_mbm_cntrs",
> + .mode = 0444,
> + .kf_ops = &rdtgroup_kf_single_ops,
> + .seq_show = resctrl_num_mbm_cntrs_show,
> + },
> {
> .name = "cpus",
> .mode = 0644,

Reinette