linux-kernel - Re: [PATCH v6 06/22] x86/resctrl: Add support to enable/disable AMD ABMC feature

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Message-ID: <aad023cb-fb80-4389-b9dc-c3468e397598@intel.com>
Date: Tue, 20 Aug 2024 11:17:27 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: <babu.moger@....com>, <corbet@....net>, <fenghua.yu@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<rdunlap@...radead.org>, <tj@...nel.org>, <peterz@...radead.org>,
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	<eranian@...gle.com>, <james.morse@....com>
Subject: Re: [PATCH v6 06/22] x86/resctrl: Add support to enable/disable AMD
 ABMC feature

Hi Babu,

On 8/19/24 11:07 AM, Moger, Babu wrote:
> Hi Reinette,
> 
> On 8/16/24 16:31, Reinette Chatre wrote:
>> Hi Babu,
>>
>> On 8/6/24 3:00 PM, Babu Moger wrote:
>>> Add the functionality to enable/disable AMD ABMC feature.
>>>
>>> AMD ABMC feature is enabled by setting enabled bit(0) in MSR
>>> L3_QOS_EXT_CFG.  When the state of ABMC is changed, the MSR needs
>>> to be updated on all the logical processors in the QOS Domain.
>>>
>>> Hardware counters will reset when ABMC state is changed. Reset the
>>
>> Could you please clarify how this works when ABMC state is changed on
>> one CPU in a domain vs all (as done in this patch) CPUs of a domain? In this
>> patch it is clear that all hardware counters are reset and consequently
>> the architectural state maintained by resctrl is reset also. Later, when
>> the code is added to handle CPU online I see that ABMC state is changed
>> on a new online CPU but I do not see matching reset of architectural state.
>> (more in that patch later)
> 
> Yes. I missed testing this scenario.
> When new cpu comes online, it should inherit the abmc state which is set
> already. it should not force it either way. In that case, it is not
> required to reset the architectural state.
> 
> I need to make few changes to make it work properly.
> 
> We need to set abmc state to "enabled" during the init when abmc is
> detected.  resctrl_late_init -> .. -> rdt_get_mon_l3_config
> 
> This only happens once during the init.
> 
> Then during the hotplug, just update the abmc state which is already set
> duing the init. This should work fine.
> 

The discussion about this flow is now split between this thread and the
discussion of patch #20. I tried to merge the discussions in my response [1]
to patch #20.

Reinette

[1] https://lore.kernel.org/lkml/6b1ad4b2-d99f-44fb-afcc-b9f48e51df6e@intel.com/