linux-kernel - Re: [PATCH v5 16/20] x86/resctrl: Report "Unassigned" for MBM events in ABMC mode

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Message-ID: <826860ab-e87a-4d2d-8b41-3487a951f759@intel.com>
Date: Fri, 12 Jul 2024 15:13:45 -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 v5 16/20] x86/resctrl: Report "Unassigned" for MBM events
 in ABMC mode

Hi Babu,

On 7/3/24 2:48 PM, Babu Moger wrote:
> In ABMC 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>
> ---
> v5: New patch.
> ---
>   Documentation/arch/x86/resctrl.rst        |  4 ++++
>   arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 19 ++++++++++++++-----
>   2 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index 4907d0758118..11b7a5f26b40 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -284,6 +284,10 @@ with the following files:
>   	until the user unassigns it manually. There is no need to worry
>   	about counters being reset during this period.
>   
> +	In ABMC mode, the MBM event counters will return "Unassigned" if
> +	the hardware counter is not assigned to the event. Users need to
> +	assign a counter manually to read the events.

This no longer seems accurate with counters assigned by default.

> +
>   	Without ABMC enabled, monitoring will work in "legacy" mode
>   	without assignment option.
>   
> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index 50fa1fe9a073..e60b469b7d12 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) {
> @@ -609,12 +609,21 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>   
>   checkresult:
>   
> -	if (rr.err == -EIO)
> +	if (rr.err == -EIO) {
>   		seq_puts(m, "Error\n");
> -	else if (rr.err == -EINVAL)
> -		seq_puts(m, "Unavailable\n");
> -	else
> +	} else if (rr.err == -EINVAL) {
> +		if (resctrl_arch_get_abmc_enabled()) {
> +			index = mon_event_config_index_get(evtid);
> +			if (rdtgrp->mon.cntr_id[index] == MON_CNTR_UNSET)
> +				seq_puts(m, "Unassigned\n");
> +			else
> +				seq_puts(m, "Unavailable\n");
> +		} else {
> +			seq_puts(m, "Unavailable\n");
> +		}
> +	} else {
>   		seq_printf(m, "%llu\n", rr.val);
> +	}
>   

This still attempts to read from hardware that is futile to do knowing
that a counter is not assigned. Why not just print "Unassigned" right away
without trying to read data from hardware when knowing it will fail?

>   out:
>   	rdtgroup_kn_unlock(of->kn);

Reinette