linux-kernel - Re: [PATCH v9 10/13] x86/resctrl: Add sysfs interface to write mbm_total_bytes

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Message-ID: <02d9ecbd-9b08-9777-f93d-0811edc79b6d@intel.com>
Date:   Tue, 20 Dec 2022 09:32:01 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     "Moger, Babu" <Babu.Moger@....com>,
        "corbet@....net" <corbet@....net>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
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Subject: Re: [PATCH v9 10/13] x86/resctrl: Add sysfs interface to write
 mbm_total_bytes_config

Hi Babu,

On 12/19/2022 11:28 AM, Moger, Babu wrote:
> [AMD Official Use Only - General]
> 
> Hi Reinette,
> 
>> -----Original Message-----
>> From: Reinette Chatre <reinette.chatre@...el.com>
>> Sent: Thursday, December 15, 2022 12:25 PM
>> To: Moger, Babu <Babu.Moger@....com>; corbet@....net;
>> tglx@...utronix.de; mingo@...hat.com; bp@...en8.de
>> Cc: fenghua.yu@...el.com; dave.hansen@...ux.intel.com; x86@...nel.org;
>> hpa@...or.com; paulmck@...nel.org; akpm@...ux-foundation.org;
>> quic_neeraju@...cinc.com; rdunlap@...radead.org;
>> damien.lemoal@...nsource.wdc.com; songmuchun@...edance.com;
>> peterz@...radead.org; jpoimboe@...nel.org; pbonzini@...hat.com;
>> chang.seok.bae@...el.com; pawan.kumar.gupta@...ux.intel.com;
>> jmattson@...gle.com; daniel.sneddon@...ux.intel.com; Das1, Sandipan
>> <Sandipan.Das@....com>; tony.luck@...el.com; james.morse@....com;
>> linux-doc@...r.kernel.org; linux-kernel@...r.kernel.org;
>> bagasdotme@...il.com; eranian@...gle.com; christophe.leroy@...roup.eu;
>> jarkko@...nel.org; adrian.hunter@...el.com; quic_jiles@...cinc.com;
>> peternewman@...gle.com
>> Subject: Re: [PATCH v9 10/13] x86/resctrl: Add sysfs interface to write
>> mbm_total_bytes_config
>>
>> Hi Babu,
>>
>> On 12/1/2022 7:37 AM, Babu Moger wrote:

...

>>> +	/*
>>> +	 * When an Event Configuration is changed, the bandwidth counters
>>> +	 * for all RMIDs and Events will be cleared by the hardware. The
>>> +	 * hardware also sets MSR_IA32_QM_CTR.Unavailable (bit 62) for
>>> +	 * every RMID on the next read to any event for every RMID.
>>> +	 * Subsequent reads will have MSR_IA32_QM_CTR.Unavailable (bit 62)
>>> +	 * cleared while it is tracked by the hardware. Clear the
>>> +	 * mbm_local and mbm_total counts for all the RMIDs.
>>> +	 */
>>> +	resctrl_arch_reset_rmid_all(r, d);
>>
>> If I understand correctly the expectation is that when user space read counters
>> (via mon_data files) right after the configuration was changed then this read
>> will return "Unavailable" and then the next read will return data.
>>
>> If this is the case then I think a snippet about this user experience would be
>> helpful to add to the documentation.
> 
> Ok.  How about this in the documentation?
> 
> "When an event configuration is changed, the bandwidth counters for all the RMIDs and the events will be cleared for that domain.
> The next read for every RMID will report "Unavailable" and subsequent reads will report the valid value."
> 
> 

Thinking about this more ... why are the counters for all eventids cleared
when only one eventid's configuration is changed?

Reinette