linux-kernel - Re: [PATCH] x86/resctrl: Fix default monitoring groups reporting

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Date:   Mon, 19 Jul 2021 13:43:42 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Babu Moger <babu.moger@....com>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <bp@...en8.de>
CC:     <fenghua.yu@...el.com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <hpa@...or.com>,
        <pawel.szulik@...el.com>, "Luck, Tony" <tony.luck@...el.com>
Subject: Re: [PATCH] x86/resctrl: Fix default monitoring groups reporting

Hi Babu,

On 6/29/2021 11:07 AM, Babu Moger wrote:
> From: Babu Moger <Babu.Moger@....com>
> 
> Creating a new sub monitoring group in the root /sys/fs/resctrl leads to
> getting the "Unavailable" value for mbm_total_bytes and mbm_local_bytes on
> the entire filesystem.
> 
> Steps to reproduce.
> 1. #mount -t resctrl resctrl /sys/fs/resctrl/
> 
> 2. #cd /sys/fs/resctrl/
> 
> 3. #cat mon_data/mon_L3_00/mbm_total_bytes 23189832
> 
> 4. #mkdir mon_groups/test1 (create sub monitor group)
> 
> 5. #cat mon_data/mon_L3_00/mbm_total_bytes Unavailable
> 
> When a new monitoring group is created, a new RMID is assigned to the new
> group. But the RMID is not active yet. When the events are read on the new
> RMID, it is expected to report the status as "Unavailable".
> 
> When the user reads the events on the default monitoring group with
> multiple subgroups, the events on all sub groups are consolidated together.
> Currently, if any of the RMID reads report as "Unavailable", then
> everything will be reported as "Unavailable".
> 
> Fix the issue by discarding the "Unavailable" reads and reporting all the
> successful RMID reads. This is not a problem on Intel systesm as Intel

systesm -> systems

> reports 0 on Inactive RMIDs.
> 
> Reported-by: Paweł Szulik <pawel.szulik@...el.com>
> Signed-off-by: Babu Moger <Babu.Moger@....com>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=213311

Is a "Fixes" available? If this is specific to AMD then could this be 
the change that enabled AMD systems?

> ---
>   arch/x86/kernel/cpu/resctrl/monitor.c |   27 +++++++++++++--------------
>   1 file changed, 13 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index dbeaa8409313..9573a30c0587 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -285,15 +285,14 @@ static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)
>   	return chunks >>= shift;
>   }
>   
> -static int __mon_event_count(u32 rmid, struct rmid_read *rr)
> +static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
>   {
>   	struct mbm_state *m;
>   	u64 chunks, tval;
>   
>   	tval = __rmid_read(rmid, rr->evtid);
>   	if (tval & (RMID_VAL_ERROR | RMID_VAL_UNAVAIL)) {
> -		rr->val = tval;
> -		return -EINVAL;
> +		return tval;
>   	}
>   	switch (rr->evtid) {
>   	case QOS_L3_OCCUP_EVENT_ID:
> @@ -305,12 +304,6 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
>   	case QOS_L3_MBM_LOCAL_EVENT_ID:
>   		m = &rr->d->mbm_local[rmid];
>   		break;
> -	default:
> -		/*
> -		 * Code would never reach here because
> -		 * an invalid event id would fail the __rmid_read.
> -		 */
> -		return -EINVAL;
>   	}
>   
>   	if (rr->first) {
> @@ -361,23 +354,29 @@ void mon_event_count(void *info)
>   	struct rdtgroup *rdtgrp, *entry;
>   	struct rmid_read *rr = info;
>   	struct list_head *head;
> +	u64 ret_val;
>   
>   	rdtgrp = rr->rgrp;
>   
> -	if (__mon_event_count(rdtgrp->mon.rmid, rr))
> -		return;
> +	ret_val = __mon_event_count(rdtgrp->mon.rmid, rr);
>   
>   	/*
> -	 * For Ctrl groups read data from child monitor groups.
> +	 * For Ctrl groups read data from child monitor groups and
> +	 * add them together. Count events which are read successfully.
> +	 * Discard the rmid_read's reporting errors.
>   	 */
>   	head = &rdtgrp->mon.crdtgrp_list;
>   
>   	if (rdtgrp->type == RDTCTRL_GROUP) {
>   		list_for_each_entry(entry, head, mon.crdtgrp_list) {
> -			if (__mon_event_count(entry->mon.rmid, rr))
> -				return;
> +			if (__mon_event_count(entry->mon.rmid, rr) == 0)
> +				ret_val = 0;
>   		}
>   	}
> +
> +	/* Report error if none of rmid_reads are successful */
> +	if (ret_val)
> +		rr->val = ret_val;
>   }
>   
>   /*
> 

With the commit message comments addressed:
Acked-by: Reinette Chatre <reinette.chatre@...el.com>

Thank you very much

Reinette