linux-kernel - Re: [PATCH v4 09/13] x86/resctrl: Add sysfs interface files to read/write event configuration

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Message-ID: <9dd5a111-63ea-8c4b-5515-d24d1d9c73f0@amd.com>
Date:   Mon, 19 Sep 2022 15:26:57 -0500
From:   "Moger, Babu" <babu.moger@....com>
To:     Reinette Chatre <reinette.chatre@...el.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,
        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
Subject: Re: [PATCH v4 09/13] x86/resctrl: Add sysfs interface files to
 read/write event configuration

Hi Reinette,

On 9/19/22 11:42, Reinette Chatre wrote:
> Hi Babu,
>
> On 9/19/2022 8:46 AM, Moger, Babu wrote:
>> Hi Reinette,
>>
>> On 9/16/22 10:58, Reinette Chatre wrote:
>>> Hi Babu,
>>>
>>> On 9/7/2022 11:01 AM, Babu Moger wrote:
>>>> Add two new sysfs files to read/write the event configuration if
>>>> the feature Bandwidth Monitoring Event Configuration (BMEC) is
>>>> supported. The file mbm_local_config is for the configuration
>>>> of the event mbm_local_bytes and the file mbm_total_config is
>>>> for the configuration of mbm_total_bytes.
>>>>
>>>> $ls /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local*
>>>> /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local_bytes
>>>> /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local_config
>>>>
>>>> $ls /sys/fs/resctrl/mon_data/mon_L3_00/mbm_total*
>>>> /sys/fs/resctrl/mon_data/mon_L3_00/mbm_total_bytes
>>>> /sys/fs/resctrl/mon_data/mon_L3_00/mbm_total_config
>>>>
>>> This patch makes the mbm*config files per monitor group. Looking
>>> ahead at later patches how the configuration is set it is not clear
>>> to me that this is the right place for these configuration files.
>>>
>>> Looking ahead to patch 10 there is neither rmid nor closid within
>>> the (MSR_IA32_EVT_CFG_BASE + index) register - it only takes
>>> the bits indicating what access types needs to be counted. Also
>>> in patch 10 I understand that the scope of this register is per L3 cache
>>> domain.
>> Yes. Scope of  MSR_IA32_EVT_CFG_BASE per L3 domain.
>>> Considering this, why is the sysfs file associated with each
>>> monitor group?
>> Please see the response below.
>>> For example, consider the following scenario:
>>> # cd /sys/fs/resctrl
>>> # mkdir g2
>>> # mkdir mon_groups/m1
>>> # mkdir mon_groups/m2
>>> # find . | grep mbm_local_config
>>> ./mon_data/mon_L3_00/mbm_local_config
>>> ./mon_data/mon_L3_01/mbm_local_config
>>> ./g2/mon_data/mon_L3_00/mbm_local_config
>>> ./g2/mon_data/mon_L3_01/mbm_local_config
>>> ./mon_groups/m2/mon_data/mon_L3_00/mbm_local_config
>>> ./mon_groups/m2/mon_data/mon_L3_01/mbm_local_config
>>> ./mon_groups/m1/mon_data/mon_L3_00/mbm_local_config
>>> ./mon_groups/m1/mon_data/mon_L3_01/mbm_local_config
>>>
>>>
>>> From what I understand, the following sysfs files are
>>> associated with cache domain #0 and thus writing to any of these
>>> files would change the same configuration:
>>> ./mon_data/mon_L3_00/mbm_local_config
>>> ./g2/mon_data/mon_L3_00/mbm_local_config
>>> ./mon_groups/m2/mon_data/mon_L3_00/mbm_local_config
>>> ./mon_groups/m1/mon_data/mon_L3_00/mbm_local_config
>>>
>>> Could you please correct me where I am wrong?
>> For example, we have CPUs 0-7 in domain 0. We have two counters which are
>> configurable.
>>
>> Lets consider same example as your mentioned about.
>>
>> g2 is a control group.
>>
>> m1 and m2 are monitor group.
>>
>> We can have control group g2 with CPUs 0-7 to limit the L3 bandwidth (or
>> memory bandwidth with required schemata setting).
>>
>> We can have mon group m1 with cpus 0-3 to monitor mbm_local_bytes.
>>
>> We can have mon group m2 with cpus  4-7 to monitor mbm_total_bytes.
>>
>> Each group is independently, monitoring two separate thing. Without having
> Right, because monitoring, the actual counting of the events, is per monitor
> group. When a monitor group is created a new RMID is created and when the
> counter is read it is per-RMID. 
>
> The event configuration is independent from the RMID using the counter.
>
>> sysfs file (mbm_local_config and mbm_total_config) in each monitor group,
>> we wont be able to configure the above configuration.
> I do not understand this reasoning. From what I understand the
> event configuration is independent from the monitoring group. Thus, changing
> an event configuration for one monitoring group would impact all
> monitoring groups using that event counter. This implementation associates
> an event configuration with each monitoring group and by doing so it
> implies that it is unique to the monitoring group, but that is not
> how it works.

The event configuration is designed per L3 domain. The mon_data is also
per domain (like mon_L3_00.. mon_L3_01 etc). So, added the event
configuration file inside each domain. We have all the information inside
the domain. Thought, that is right place. I am open for suggestions.

Thanks

Babu