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Message-ID: <48d8a630-0d77-45b1-8951-6dd62185953d@amd.com>
Date: Wed, 25 Jun 2025 15:33:42 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.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,
rostedt@...dmis.org, paulmck@...nel.org, thuth@...hat.com, ardb@...nel.org,
gregkh@...uxfoundation.org, seanjc@...gle.com, thomas.lendacky@....com,
pawan.kumar.gupta@...ux.intel.com, manali.shukla@....com,
perry.yuan@....com, kai.huang@...el.com, peterz@...radead.org,
xiaoyao.li@...el.com, kan.liang@...ux.intel.com, mario.limonciello@....com,
xin3.li@...el.com, gautham.shenoy@....com, xin@...or.com,
chang.seok.bae@...el.com, fenghuay@...dia.com, peternewman@...gle.com,
maciej.wieczor-retman@...el.com, eranian@...gle.com,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v14 12/32] fs/resctrl: Introduce interface to display
number of assignable counter IDs
Hi Reinette,
On 6/24/25 18:05, Reinette Chatre wrote:
> Hi Babu,
>
> There seems to be many places referring to user space assigning "counter IDs",
> as I understand the interface the user has no control over the actual ID of the
> counter being assigned. Please correct me if I am wrong.
Yes. Agree. Users have no control over which counter is assigned.
> Considering this, how about:
> fs/resctrl: Add resctrl file to display number of assignable counters
>
> If you agree, please check the whole series as this seems to be an often
> copy&pasted term.
Yes. Sure.
>
> On 6/13/25 2:04 PM, Babu Moger wrote:
>> The "mbm_event" mode allows users to assign a hardware counter ID to an
>
> "a hardware counter ID" -> "a hardware counter"?
>
>> RMID, event pair and monitor bandwidth usage as long as it is assigned.
>> The hardware continues to track the assigned counter until it is
>> explicitly unassigned by the user.
>>
>> Create 'num_mbm_cntrs' resctrl file that displays the number of counter
>> IDs supported in each domain. 'num_mbm_cntrs' is only visible to user
>
> "number of counter IDs" -> "number of counters"?
>
>> space when the system supports "mbm_event" mode.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>
> ...
>
>> ---
>> Documentation/filesystems/resctrl.rst | 11 ++++++++++
>> fs/resctrl/monitor.c | 4 ++++
>> fs/resctrl/rdtgroup.c | 30 +++++++++++++++++++++++++++
>> 3 files changed, 45 insertions(+)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index 4e76e4ac5d3a..801914de0c81 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -288,6 +288,17 @@ with the following files:
>> result in misleading values or display "Unavailable" if no counter is assigned
>> to the event.
>>
>> +"num_mbm_cntrs":
>> + The maximum number of counter IDs (total of available and assigned counters)
>
> "number of counter IDs" -> "number of counters"
Sure.
>
>> + in each domain when the system supports mbm_event 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/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
>> index dcc6c00eb362..92a87aa97b0f 100644
>> --- a/fs/resctrl/monitor.c
>> +++ b/fs/resctrl/monitor.c
>> @@ -924,6 +924,10 @@ int resctrl_mon_resource_init(void)
>> else if (resctrl_is_mon_event_enabled(QOS_L3_MBM_TOTAL_EVENT_ID))
>> 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 | RFTYPE_RES_CACHE);
>> +
>> return 0;
>> }
>>
>> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
>> index ba7a9a68c5a6..967e4df62a19 100644
>> --- a/fs/resctrl/rdtgroup.c
>> +++ b/fs/resctrl/rdtgroup.c
>> @@ -1829,6 +1829,30 @@ 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 = rdt_kn_parent_priv(of->kn);
>> + 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_putc(s, ';');
>> +
>> + seq_printf(s, "%d=%d", dom->hdr.id, r->mon.num_mbm_cntrs);
>> + sep = true;
>> + }
>> + seq_putc(s, '\n');
>> +
>> + mutex_unlock(&rdtgroup_mutex);
>> + cpus_read_unlock();
>> + return 0;
>> +}
>> +
>> /* rdtgroup information files for one cache resource. */
>> static struct rftype res_common_files[] = {
>> {
>> @@ -1866,6 +1890,12 @@ static struct rftype res_common_files[] = {
>> .seq_show = rdt_default_ctrl_show,
>> .fflags = RFTYPE_CTRL_INFO | RFTYPE_RES_CACHE,
>> },
>> + {
>> + .name = "num_mbm_cntrs",
>> + .mode = 0444,
>> + .kf_ops = &rdtgroup_kf_single_ops,
>> + .seq_show = resctrl_num_mbm_cntrs_show,
>> + },
>> {
>> .name = "min_cbm_bits",
>> .mode = 0444,
>
> Patch looks good.
>
> Reinette
>
--
Thanks
Babu Moger
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