linux-kernel - Re: [PATCH v7 19/24] x86/resctrl: Report "Unassigned" for MBM events in mbm_cntr

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Message-ID: <f5f61804-3743-42ef-83ed-6c198c4eef74@intel.com>
Date: Thu, 19 Sep 2024 10:31:14 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <fenghua.yu@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<rdunlap@...radead.org>, <tj@...nel.org>, <peterz@...radead.org>,
	<yanjiewtw@...il.com>, <kim.phillips@....com>, <lukas.bulwahn@...il.com>,
	<seanjc@...gle.com>, <jmattson@...gle.com>, <leitao@...ian.org>,
	<jpoimboe@...nel.org>, <rick.p.edgecombe@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <jithu.joseph@...el.com>,
	<kai.huang@...el.com>, <kan.liang@...ux.intel.com>,
	<daniel.sneddon@...ux.intel.com>, <pbonzini@...hat.com>,
	<sandipan.das@....com>, <ilpo.jarvinen@...ux.intel.com>,
	<peternewman@...gle.com>, <maciej.wieczor-retman@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<eranian@...gle.com>, <james.morse@....com>
Subject: Re: [PATCH v7 19/24] x86/resctrl: Report "Unassigned" for MBM events
 in mbm_cntr_assign mode

Hi Babu,

On 9/4/24 3:21 PM, Babu Moger wrote:
> In mbm_cntr_assign mode, the hardware counter should be assigned to read
> the MBM events.
> 
> Report "Unassigned" in case the user attempts to read the events without
> assigning the counter.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
> v7: Moved the documentation under "mon_data".
>     Updated the text little bit.
> 
> v6: Added more explaination in the resctrl.rst
>     Added checks to detect "Unassigned" before reading RMID.
> 
> v5: New patch.
> ---
>  Documentation/arch/x86/resctrl.rst        | 10 ++++++++++
>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 13 ++++++++++++-
>  2 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index 3e9302971faf..ff5397d19704 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -417,6 +417,16 @@ When monitoring is enabled all MON groups will also contain:
>  	for the L3 cache they occupy). These are named "mon_sub_L3_YY"
>  	where "YY" is the node number.
>  
> +	The mbm_cntr_assign mode allows users to assign a hardware counter
> +	to an RMID-event pair, enabling bandwidth monitoring for as long
> +	as the counter remains assigned. The hardware will continue tracking
> +	the assigned RMID until the user manually unassigns it, ensuring
> +	that counters are not reset during this period. With a limited number
> +	of counters, the system may run out of assignable resources. In
> +	mbm_cntr_assign mode, MBM event counters will return "Unassigned"
> +	if the counter is not allocated to the event when read. Users must
> +	manually assign a counter to read the events.
> +

Please consider how this text could also be relevant to soft-ABMC.

>  "mon_hw_id":
>  	Available only with debug option. The identifier used by hardware
>  	for the monitor group. On x86 this is the RMID.
> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index 50fa1fe9a073..fc19b1d131b2 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -562,7 +562,7 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>  	struct rdtgroup *rdtgrp;
>  	struct rdt_resource *r;
>  	union mon_data_bits md;
> -	int ret = 0;
> +	int ret = 0, index;
>  
>  	rdtgrp = rdtgroup_kn_lock_live(of->kn);
>  	if (!rdtgrp) {
> @@ -576,6 +576,15 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>  	evtid = md.u.evtid;
>  	r = &rdt_resources_all[resid].r_resctrl;
>  
> +	if (resctrl_arch_mbm_cntr_assign_enabled(r) && evtid != QOS_L3_OCCUP_EVENT_ID) {
> +		index = mon_event_config_index_get(evtid);

This should use MBM_EVENT_ARRAY_INDEX, not the arch index.

> +		if (index != INVALID_CONFIG_INDEX &&
> +		    rdtgrp->mon.cntr_id[index] == MON_CNTR_UNSET) {
> +			rr.err = -ENOENT;
> +			goto checkresult;
> +		}
> +	}
> +
>  	if (md.u.sum) {
>  		/*
>  		 * This file requires summing across all domains that share
> @@ -613,6 +622,8 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>  		seq_puts(m, "Error\n");
>  	else if (rr.err == -EINVAL)
>  		seq_puts(m, "Unavailable\n");
> +	else if (rr.err == -ENOENT)
> +		seq_puts(m, "Unassigned\n");
>  	else
>  		seq_printf(m, "%llu\n", rr.val);
>  

Reinette