Re: [PATCH v12 03/26] x86/cpufeatures: Add support for Assignable Bandwidth Monitoring Counters (ABMC)

Reinette Chatre
2025-04-15T16:09:40Z

Hi Babu,

On 4/14/25 10:48 AM, Moger, Babu wrote:

> Here is my proposal to handle this case. This can be separate patch.
>
>
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index d10cf1e5b914..772f2f77faee 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1370,7 +1370,7 @@ static int rdt_mon_features_show(struct
> kernfs_open_file *of,
>
> list_for_each_entry(mevt, &r->mon.evt_list, list) {
> seq_printf(seq, "%s\n", mevt->name);
> - if (mevt->configurable)
> + if (mevt->configurable &&
> !resctrl_arch_mbm_cntr_assign_enabled(r))
> seq_printf(seq, "%s_config\n", mevt->name);
> }
>
> @@ -1846,6 +1846,11 @@ static int mbm_config_show(struct seq_file *s,
> struct rdt_resource *r, u32 evtid
> cpus_read_lock();
> mutex_lock(&rdtgroup_mutex);
>
> + if (resctrl_arch_mbm_cntr_assign_enabled(r)) {
> + rdt_last_cmd_puts("Event configuration(BMEC) not supported
> with mbm_cntr_assign mode\n");
> + return -EINVAL;
> + }
> +
> list_for_each_entry(dom, &r->mon_domains, hdr.list) {
> if (sep)
> seq_puts(s, ";");
> @@ -1865,21 +1870,24 @@ static int mbm_config_show(struct seq_file *s,
> struct rdt_resource *r, u32 evtid
> static int mbm_total_bytes_config_show(struct kernfs_open_file *of,
> struct seq_file *seq, void *v)
> {
> + int ret;
> struct rdt_resource *r = of->kn->parent->priv;
>
> - mbm_config_show(seq, r, QOS_L3_MBM_TOTAL_EVENT_ID);
> + ret = mbm_config_show(seq, r, QOS_L3_MBM_TOTAL_EVENT_ID);
>
> - return 0;
> + return ret;
> }
>
> static int mbm_local_bytes_config_show(struct kernfs_open_file *of,
> struct seq_file *seq, void *v)
> {
> + int ret;
> +
> struct rdt_resource *r = of->kn->parent->priv;
>
> - mbm_config_show(seq, r, QOS_L3_MBM_LOCAL_EVENT_ID);
> + ret = mbm_config_show(seq, r, QOS_L3_MBM_LOCAL_EVENT_ID);
>
> - return 0;
> + return ret;
> }
>
> static void mbm_config_write_domain(struct rdt_resource *r,
> @@ -1932,6 +1940,11 @@ static int mon_config_write(struct rdt_resource *r,
> char *tok, u32 evtid)
> /* Walking r->domains, ensure it can't race with cpuhp */
> lockdep_assert_cpus_held();
>
> + if (resctrl_arch_mbm_cntr_assign_enabled(r)) {
> + rdt_last_cmd_puts("Event configuration(BMEC) not supported
> with mbm_cntr_assign mode\n");
> + return -EINVAL;
> + }
> +
> next:
> if (!tok || tok[0] == '\0')
> return 0;
>

Instead of chasing every call that may involve BMEC I think it will be simpler to
disable BMEC support during initialization when ABMC is detected. Specifically,
on systems that support both BMEC and ABMC rdt_cpu_has(X86_FEATURE_BMEC) returns
false.

I would also like to consider enhancing mevt->configurable to handle all different
ways in which events can be configured. For example, making mevt->configurable an
enum that captures how event can be configured instead of keeping mevt->configurable
a boolean for BMEC support and handling ABMC completely separately. I hope this
may become clearer when using struct mon_evt for ABMC also.

Reinette