linux-kernel - Re: [PATCH v15 21/34] x86/resctrl: Refactor resctrl_arch_rmid

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Message-ID: <cd5bc14a-8b96-40ac-bd5f-7ecedd1d3464@amd.com>
Date: Tue, 22 Jul 2025 09:23:41 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tony.luck@...el.com, james.morse@....com, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com
Cc: Dave.Martin@....com, x86@...nel.org, hpa@...or.com,
 akpm@...ux-foundation.org, paulmck@...nel.org, rostedt@...dmis.org,
 Neeraj.Upadhyay@....com, david@...hat.com, arnd@...db.de, fvdl@...gle.com,
 seanjc@...gle.com, jpoimboe@...nel.org, pawan.kumar.gupta@...ux.intel.com,
 xin@...or.com, manali.shukla@....com, tao1.su@...ux.intel.com,
 sohil.mehta@...el.com, kai.huang@...el.com, xiaoyao.li@...el.com,
 peterz@...radead.org, xin3.li@...el.com, kan.liang@...ux.intel.com,
 mario.limonciello@....com, thomas.lendacky@....com, perry.yuan@....com,
 gautham.shenoy@....com, chang.seok.bae@...el.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, peternewman@...gle.com, eranian@...gle.com
Subject: Re: [PATCH v15 21/34] x86/resctrl: Refactor resctrl_arch_rmid_read()

Hi Reinette,


On 7/17/25 22:51, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/8/25 3:17 PM, Babu Moger wrote:
>> resctrl_arch_rmid_read() modifies the value obtained from MSR_IA32_QM_CTR
>> to account for overflow. This adjustment is common to both
> 
> The portion factored out does not just handle MBM overflow counts but also
> handles counter scaling for *all* events, including cache occupancy.

Yes. Got it. thanks

> 
>> resctrl_arch_rmid_read() and resctrl_arch_cntr_read().
>>
>> To prepare for the implementation of resctrl_arch_cntr_read(), refactor
>> this logic into a new function called mbm_corrected_val().
> 
> This thus cannot be made specific to MBM. More accurate may be
> get_corrected_val().

Sure.

Rephrased the changelog.

x86/resctrl: Refactor resctrl_arch_rmid_read()

resctrl_arch_rmid_read() modifies the value obtained from MSR_IA32_QM_CTR
to account for the overflow for MBM events and apply counter scaling for
all the events. This logic is common to both resctrl_arch_rmid_read() and
resctrl_arch_cntr_read().

To prepare for the implementation of resctrl_arch_cntr_read(), refactor
this logic into a new function called get_corrected_val().

Signed-off-by: Babu Moger <babu.moger@....com>



> 
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>> v15: New patch to add arch calls resctrl_arch_cntr_read() and resctrl_arch_reset_cntr()
>>      with mbm_event mode.
>>      https://lore.kernel.org/lkml/b4b14670-9cb0-4f65-abd5-39db996e8da9@intel.com/
>> ---
>>  arch/x86/kernel/cpu/resctrl/monitor.c | 38 ++++++++++++++++-----------
>>  1 file changed, 23 insertions(+), 15 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 017f3b8e28f9..a230d98e9d73 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -217,15 +217,33 @@ static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)
>>  	return chunks >> shift;
>>  }
>>  
>> +static u64 mbm_corrected_val(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +			     u32 rmid, enum resctrl_event_id eventid, u64 msr_val)
>> +{
>> +	struct rdt_hw_mon_domain *hw_dom = resctrl_to_arch_mon_dom(d);
>> +	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>> +	struct arch_mbm_state *am;
>> +	u64 chunks;
>> +
>> +	am = get_arch_mbm_state(hw_dom, rmid, eventid);
>> +	if (am) {
> 
> These are MBM counter adjustments.
Sure.

> 
>> +		am->chunks += mbm_overflow_count(am->prev_msr, msr_val,
>> +				hw_res->mbm_width);
> 
> Above can be aligned to open parentheses.

Yes.

> 
>> +		chunks = get_corrected_mbm_count(rmid, am->chunks);
>> +		am->prev_msr = msr_val;
>> +	} else {
> 
> Cache occupancy handled here.
> 

Sure.

>> +		chunks = msr_val;
>> +	}
>> +
> Both MBM and cache occupancy scaled below:

Yes.

>> +	return chunks * hw_res->mon_scale;
>> +}
>> +
>>  int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_mon_domain *d,
>>  			   u32 unused, u32 rmid, enum resctrl_event_id eventid,
>>  			   u64 *val, void *ignored)
>>  {
>> -	struct rdt_hw_mon_domain *hw_dom = resctrl_to_arch_mon_dom(d);
>> -	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>>  	int cpu = cpumask_any(&d->hdr.cpu_mask);
>> -	struct arch_mbm_state *am;
>> -	u64 msr_val, chunks;
>> +	u64 msr_val;
>>  	u32 prmid;
>>  	int ret;
>>  
>> @@ -236,17 +254,7 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_mon_domain *d,
>>  	if (ret)
>>  		return ret;
>>  
>> -	am = get_arch_mbm_state(hw_dom, rmid, eventid);
>> -	if (am) {
>> -		am->chunks += mbm_overflow_count(am->prev_msr, msr_val,
>> -						 hw_res->mbm_width);
>> -		chunks = get_corrected_mbm_count(rmid, am->chunks);
>> -		am->prev_msr = msr_val;
>> -	} else {
>> -		chunks = msr_val;
>> -	}
>> -
>> -	*val = chunks * hw_res->mon_scale;
>> +	*val = mbm_corrected_val(r, d, rmid, eventid, msr_val);
>>  
>>  	return 0;
>>  }
> 
> Reinette
> 

-- 
Thanks
Babu Moger