Message-ID: <0f10bc24-b10d-4834-9643-5e44a2b83f74@intel.com>
Date: Wed, 25 Jun 2025 16:40:14 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <akpm@...ux-foundation.org>,
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	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v14 31/32] fs/resctrl: Introduce the interface to switch
 between monitor modes

Hi Babu,

On 6/13/25 2:05 PM, Babu Moger wrote:
> Resctrl subsystem can support two monitoring modes, "mbm_event" or
> "default". In mbm_event mode, monitoring event can only accumulate data
> while it is backed by a hardware counter. In "default" mode, resctrl
> assumes there is a hardware counter for each event within every CTRL_MON
> and MON group.
> 
> Introduce interface to switch between mbm_event and default modes.

"Introduce interface" -> "Introduce mbm_assign_mode resctrl file"

> 
> Example:
> To list the MBM monitor modes supported:
> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> [mbm_event]
> default
> 
> To enable the "mbm_event" monitoring mode:
> $ echo "mbm_event" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> 
> To enable the "default" monitoring mode:
> $ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> 
> MBM event counters are automatically reset as part of changing the mode.
> Clear both architectural and non-architectural event states to prevent
> overflow conditions during the next event read. Also clear assignable
> counter configuration on all the domains.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---

...

> ---
>  Documentation/filesystems/resctrl.rst | 23 +++++++-
>  fs/resctrl/internal.h                 |  2 +
>  fs/resctrl/monitor.c                  | 27 ++++++++++
>  fs/resctrl/rdtgroup.c                 | 78 +++++++++++++++++++++++++--
>  4 files changed, 126 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index cd82c2966ed7..7e62c7fdcefa 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -259,7 +259,9 @@ with the following files:
>  
>  "mbm_assign_mode":
>  	The supported monitoring modes. The enclosed brackets indicate which mode
> -	is enabled.
> +	is enabled. The MBM events (mbm_total_bytes and/or mbm_local_bytes) associated

Since there may be more events in future I think the "(mbm_total_bytes and/or
mbm_local_bytes)" can be dropped.

> +	with counters may reset when "mbm_assign_mode" is changed.
> +
>  	::
>  
>  	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> @@ -279,6 +281,15 @@ with the following files:
>  	of counters available is described in the "num_mbm_cntrs" file. Changing the
>  	mode may cause all counters on the resource to reset.
>  
> +	Moving to mbm_event mode require users to assign the counters to the events.

"Moving to mbm_event mode require" -> "mbm_event counter assignment mode requires"

> +	Otherwise, the MBM event counters will return 'Unassigned' when read.
> +
> +	The mode is beneficial for AMD platforms that support more CTRL_MON
> +	and MON groups than available hardware counters. By default, this
> +	feature is enabled on AMD platforms with the ABMC (Assignable Bandwidth
> +	Monitoring Counters) capability, ensuring counters remain assigned even
> +	when the corresponding RMID is not actively used by any processor.
> +
>  	"default":
>  
>  	In default mode, resctrl assumes there is a hardware counter for each
> @@ -288,6 +299,16 @@ with the following files:
>  	result in misleading values or display "Unavailable" if no counter is assigned
>  	to the event.
>  
> +	* To enable "mbm_event" monitoring mode:
> +	  ::
> +
> +	    # echo "mbm_event" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> +
> +	* To enable "default" monitoring mode:
> +	  ::
> +
> +	    # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> +
>  "num_mbm_cntrs":
>  	The maximum number of counter IDs (total of available and assigned counters)
>  	in each domain when the system supports mbm_event mode.
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index 14d99c723ea5..adc9ff3efdfd 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -414,6 +414,8 @@ void resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *
>  				 struct rdtgroup *rdtgrp, struct mon_evt *mevt);
>  int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
>  		 struct rdtgroup *rdtgrp, enum resctrl_event_id evtid);
> +void resctrl_reset_rmid_all(struct rdt_resource *r, struct rdt_mon_domain *d);
> +void mbm_cntr_free_all(struct rdt_resource *r, struct rdt_mon_domain *d);
>  
>  #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
>  int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 618c94cd1ad8..504b869570e6 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -1045,6 +1045,33 @@ static void mbm_cntr_free(struct rdt_mon_domain *d, int cntr_id)
>  	memset(&d->cntr_cfg[cntr_id], 0, sizeof(struct mbm_cntr_cfg));
>  }
>  
> +/**
> + * mbm_cntr_free_all() - Clear all the counter ID configuration details in the
> + *			 domain @d. Called when mbm_assign_mode is changed.
> + */
> +void mbm_cntr_free_all(struct rdt_resource *r, struct rdt_mon_domain *d)
> +{
> +	memset(d->cntr_cfg, 0, sizeof(*d->cntr_cfg) * r->mon.num_mbm_cntrs);
> +}
> +
> +/**
> + * resctrl_reset_rmid_all() - Reset all non-architecture states for all the
> + *			      supported RMIDs.
> + */
> +void resctrl_reset_rmid_all(struct rdt_resource *r, struct rdt_mon_domain *d)

struct rdt_resource *r is unused? At this time it seems unnecessary to check if
an MBM event belongs to particular resource since at this point I expect only L3
is possible. Even so, to be consistent and robust I think it would make flows
easier to understand by always ensureing that mon_evt::rid matches
expected resource.

> +{
> +	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
> +	enum resctrl_event_id evt;
> +	int idx;
> +
> +	for_each_mbm_event_id(evt) {
> +		if (!resctrl_is_mon_event_enabled(evt))
> +			continue;
> +		idx = MBM_STATE_IDX(evt);
> +		memset(d->mbm_states[idx], 0, sizeof(struct mbm_state) * idx_limit);

sizeof(*d->mbm_states[0])?

> +	}
> +}
> +
>  /**
>   * resctrl_alloc_config_cntr() - Allocate a counter ID and configure it for the
>   * event pointed to by @mevt and the resctrl group @rdtgrp within the domain @d.
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index 8c67e0897f25..6bb61fcf8673 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -1876,6 +1876,77 @@ static int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
>  	return 0;
>  }
>  
> +static ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of,
> +					     char *buf, size_t nbytes, loff_t off)
> +{
> +	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
> +	struct rdt_mon_domain *d;
> +	int ret = 0;
> +	bool enable;
> +
> +	/* 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 (!strcmp(buf, "default")) {
> +		enable = 0;
> +	} else if (!strcmp(buf, "mbm_event")) {
> +		if (r->mon.mbm_cntr_assignable) {
> +			enable = 1;
> +		} else {
> +			ret = -EINVAL;
> +			rdt_last_cmd_puts("mbm_event mode is not supported\n");
> +			goto write_exit;

write_exit -> out_unlock

> +		}
> +	} else {
> +		ret = -EINVAL;
> +		rdt_last_cmd_puts("Unsupported assign mode\n");
> +		goto write_exit;
> +	}
> +
> +	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
> +		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
> +		if (ret)
> +			goto write_exit;
> +
> +		/* Update the visibility of BMEC related files */
> +		resctrl_bmec_files_show(r, !enable);
> +
> +		/*
> +		 * Initialize the default memory transaction values for
> +		 * total and local events.
> +		 */
> +		if (resctrl_is_mon_event_enabled(QOS_L3_MBM_TOTAL_EVENT_ID))
> +			resctrl_set_mon_evt_cfg(QOS_L3_MBM_TOTAL_EVENT_ID,
> +						MAX_EVT_CONFIG_BITS);
> +		if (resctrl_is_mon_event_enabled(QOS_L3_MBM_LOCAL_EVENT_ID))
> +			resctrl_set_mon_evt_cfg(QOS_L3_MBM_LOCAL_EVENT_ID,
> +						READS_TO_LOCAL_MEM |
> +						READS_TO_LOCAL_S_MEM |
> +						NON_TEMP_WRITE_TO_LOCAL_MEM);

Nice, yes, this belongs in resctrl fs.

> +		/*
> +		 * Reset all the non-achitectural RMID state and assignable counters.
> +		 */
> +		list_for_each_entry(d, &r->mon_domains, hdr.list) {
> +			mbm_cntr_free_all(r, d);
> +			resctrl_reset_rmid_all(r, d);
> +		}
> +	}
> +
> +write_exit:
> +	mutex_unlock(&rdtgroup_mutex);
> +	cpus_read_unlock();
> +
> +	return ret ?: nbytes;
> +}
> +
>  static int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
>  				      struct seq_file *s, void *v)
>  {
> @@ -2203,8 +2274,8 @@ static int resctrl_process_assign(struct rdt_resource *r, struct rdtgroup *rdtgr
>  	struct mon_evt *mevt;
>  	int assign_state;
>  	char domain[10];
> +	int ret = 0;
>  	bool found;
> -	int ret;
>  
>  	mevt = mbm_get_mon_event_by_name(r, event);
>  	if (!mevt) {
> @@ -2249,7 +2320,7 @@ static int resctrl_process_assign(struct rdt_resource *r, struct rdtgroup *rdtgr
>  
>  	switch (assign_state) {
>  	case ASSIGN_NONE:
> -		ret = resctrl_unassign_cntr_event(r, d, rdtgrp, mevt);
> +		resctrl_unassign_cntr_event(r, d, rdtgrp, mevt);
>  		break;
>  	case ASSIGN_EXCLUSIVE:
>  		ret = resctrl_assign_cntr_event(r, d, rdtgrp, mevt);

Two stray hunks?

> @@ -2463,9 +2534,10 @@ static struct rftype res_common_files[] = {
>  	},
>  	{
>  		.name		= "mbm_assign_mode",
> -		.mode		= 0444,
> +		.mode		= 0644,
>  		.kf_ops		= &rdtgroup_kf_single_ops,
>  		.seq_show	= resctrl_mbm_assign_mode_show,
> +		.write		= resctrl_mbm_assign_mode_write,
>  		.fflags		= RFTYPE_MON_INFO | RFTYPE_RES_CACHE,
>  	},
>  	{

Reinette

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