Re: [PATCH v13 20/27] x86/resctrl: Provide interface to update the event configurations

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

Hi Babu,

On 5/15/25 3:52 PM, Babu Moger wrote:
> Users can modify the event configuration by writing to the event_filter
> interface file. The event configurations for mbm_cntr_assign mode are
> located in /sys/fs/resctrl/info/event_configs/.

heh ... looks like you also started thinking that "event_configs"
is a better name (also missing L3_MON).

> 
> Update the assignments of all groups when the event configuration is
> modified.
> 
> Example:
> $ cd /sys/fs/resctrl/
> 
> $ cat info/L3_MON/counter_configs/mbm_local_bytes/event_filter
>   local_reads,local_non_temporal_writes,local_reads_slow_memory
> 
> $ echo "local_reads,local_non_temporal_writes" >
>   info/L3_MON/counter_configs/mbm_total_bytes/event_filter
> 
> $ cat info/L3_MON/counter_configs/mbm_total_bytes/event_filter
>   local_reads,local_non_temporal_writes
> 
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
> v13: Updated changelog for imperative mode.
>      Added function description in the prototype.
>      Updated the user doc resctrl.rst to address few feedback.
>      Resolved conflicts caused by the recent FS/ARCH code restructure.
>      The rdtgroup.c/monitor.c file has now been split between the FS and ARCH directories.
> 
> v12: New patch to modify event configurations.
> ---
>  Documentation/filesystems/resctrl.rst |  12 +++
>  fs/resctrl/rdtgroup.c                 | 120 +++++++++++++++++++++++++-
>  2 files changed, 131 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index 4eb9f007ba3d..9923276826db 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst

...

> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index cf84e3a382ac..8c498b41be5d 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -1930,6 +1930,123 @@ static int event_filter_show(struct kernfs_open_file *of, struct seq_file *seq,
>  	return 0;
>  }
>  
> +/**
> + * resctrl_group_assign - Update the counter assignments for the event in
> + *			  a group.

This name is very generic with an unexpected namespace. "rdtgroup_" prefix
is often used for a function that operates on a rdtgroup. This can thus be
"rdtgroup_assign_cntr()".

> + * @r:		Resource to which update needs to be done.
> + * @rdtgrp:	Resctrl group.
> + * @evtid:	Event ID.
> + * @evt_cfg:	Event configuration value.
> + */
> +static int resctrl_group_assign(struct rdt_resource *r, struct rdtgroup *rdtgrp,
> +				enum resctrl_event_id evtid, u32 evt_cfg)
> +{
> +	struct rdt_mon_domain *d;
> +	int cntr_id;
> +
> +	list_for_each_entry(d, &r->mon_domains, hdr.list) {
> +		cntr_id = mbm_cntr_get(r, d, rdtgrp, evtid);
> +		if (cntr_id >= 0 && d->cntr_cfg[cntr_id].evt_cfg != evt_cfg) {
> +			d->cntr_cfg[cntr_id].evt_cfg = evt_cfg;
> +			resctrl_arch_config_cntr(r, d, evtid, rdtgrp->mon.rmid,
> +						 rdtgrp->closid, cntr_id, evt_cfg, true);
> +		}
> +	}
> +
> +	return 0;

Can just return void?

> +}
> +
> +/**
> + * resctrl_update_assign - Update the counter assignments for the event for all
> + *			   the groups.

Again very generic with "update" and "assign" that seem redundant? How about
"resctrl_assign_cntr_allrdtgrp()"?

> + * @r:		Resource to which update needs to be done.
> + * @evtid:	Event ID.
> + * @evt_cfg:	Event configuration value.

Why are both event ID and evt_cfg needed? Could just passing mon_evt simplify this?

> + */
> +static int resctrl_update_assign(struct rdt_resource *r, enum resctrl_event_id evtid,
> +				 u32 evt_cfg)
> +{
> +	struct rdtgroup *prgrp, *crgrp;
> +
> +	/* Check if the cntr_id is associated to the event type updated */

Comment does not match code.

> +	list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
> +		resctrl_group_assign(r, prgrp, evtid, evt_cfg);
> +
> +		list_for_each_entry(crgrp, &prgrp->mon.crdtgrp_list, mon.crdtgrp_list) {
> +			resctrl_group_assign(r, crgrp, evtid, evt_cfg);
> +		}

Unnecessary braces?

> +	}
> +
> +	return 0;

return void?

> +}
> +
> +static int resctrl_process_configs(char *tok, u32 *val)
> +{
> +	char *evt_str;
> +	bool found;
> +	int i;
> +
> +next_config:
> +	if (!tok || tok[0] == '\0')
> +		return 0;
> +
> +	/* Start processing the strings for each event type */

Does comment intend to describe one iteration or all iterations?
Also, "event type" -> "memory transaction"?

> +	evt_str = strim(strsep(&tok, ","));
> +	found = false;
> +	for (i = 0; i < NUM_MBM_EVT_VALUES; i++) {
> +		if (!strcmp(mbm_evt_values[i].evt_name, evt_str)) {
> +			*val |=  mbm_evt_values[i].evt_val;

check spacing.

> +			found = true;
> +			break;
> +		}
> +	}
> +
> +	if (!found) {
> +		rdt_last_cmd_printf("Invalid event type %s\n", evt_str);
> +		return -EINVAL;

Looks like this will return partially initialized data. Please use a local
variable in which to gather the new configuration and only assign that
to provided pointer on success.

> +	}
> +
> +	goto next_config;
> +}
> +
> +static ssize_t event_filter_write(struct kernfs_open_file *of, char *buf,
> +				  size_t nbytes, loff_t off)
> +{
> +	struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
> +	struct mon_evt *mevt = rdt_kn_parent_priv(of->kn);
> +	u32 evt_cfg = 0;
> +	int ret = 0;
> +
> +	/* Valid input requires a trailing newline */
> +	if (nbytes == 0 || buf[nbytes - 1] != '\n')
> +		return -EINVAL;
> +
> +	buf[nbytes - 1] = '\0';
> +
> +	cpus_read_lock();
> +	mutex_lock(&rdtgroup_mutex);
> +
> +	rdt_last_cmd_clear();
> +
> +	if (!resctrl_arch_mbm_cntr_assign_enabled(r)) {
> +		rdt_last_cmd_puts("mbm_cntr_assign mode is not enabled\n");
> +		ret = -EINVAL;
> +		goto unlock_out;

"grep goto fs/resctrl/rdtgroup.c"

> +	}
> +
> +	ret = resctrl_process_configs(buf, &evt_cfg);
> +	if (!ret && mevt->evt_val != evt_cfg) {
> +		mevt->evt_val = evt_cfg;

ah ... here it is. hmmm ... but it is mon_evt::evt_cfg, no? ah,
fixed in next patch.

I still seem to be missing something because I expected mon_evt::evt_cfg
of mbm_total_bytes and mbm_local_bytes to be initialized with a starting
default. I missed where this is done in this series.

> +		resctrl_update_assign(r, mevt->evtid, evt_cfg);
> +	}
> +
> +unlock_out:
> +	mutex_unlock(&rdtgroup_mutex);
> +	cpus_read_unlock();
> +
> +	return ret ?: nbytes;
> +}
> +
>  /* rdtgroup information files for one cache resource. */
>  static struct rftype res_common_files[] = {
>  	{
> @@ -2056,9 +2173,10 @@ static struct rftype res_common_files[] = {
>  	},
>  	{
>  		.name		= "event_filter",
> -		.mode		= 0444,
> +		.mode		= 0644,
>  		.kf_ops		= &rdtgroup_kf_single_ops,
>  		.seq_show	= event_filter_show,
> +		.write		= event_filter_write,
>  	},
>  	{
>  		.name		= "mbm_assign_mode",

Reinette