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SubjectRe: [PATCH v9 10/13] x86/resctrl: Add sysfs interface to write mbm_total_bytes_config
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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@intel.com>
>> Sent: Thursday, December 15, 2022 12:25 PM
>> To: Moger, Babu <Babu.Moger@amd.com>; corbet@lwn.net;
>> tglx@linutronix.de; mingo@redhat.com; bp@alien8.de
>> Cc: fenghua.yu@intel.com; dave.hansen@linux.intel.com; x86@kernel.org;
>> hpa@zytor.com; paulmck@kernel.org; akpm@linux-foundation.org;
>> quic_neeraju@quicinc.com; rdunlap@infradead.org;
>> damien.lemoal@opensource.wdc.com; songmuchun@bytedance.com;
>> peterz@infradead.org; jpoimboe@kernel.org; pbonzini@redhat.com;
>> chang.seok.bae@intel.com; pawan.kumar.gupta@linux.intel.com;
>> jmattson@google.com; daniel.sneddon@linux.intel.com; Das1, Sandipan
>> <Sandipan.Das@amd.com>; tony.luck@intel.com; james.morse@arm.com;
>> linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org;
>> bagasdotme@gmail.com; eranian@google.com; christophe.leroy@csgroup.eu;
>> jarkko@kernel.org; adrian.hunter@intel.com; quic_jiles@quicinc.com;
>> peternewman@google.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


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