linux-kernel - Re: [PATCH v7 15/24] x86/resctrl: Implement resctrl_arch_assign

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Message-ID: <39d8602d-e4e2-4b27-9e94-e30afce96a64@amd.com>
Date: Tue, 24 Sep 2024 09:07:11 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.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, yanjiewtw@...il.com,
 kim.phillips@....com, lukas.bulwahn@...il.com, seanjc@...gle.com,
 jmattson@...gle.com, leitao@...ian.org, jpoimboe@...nel.org,
 rick.p.edgecombe@...el.com, kirill.shutemov@...ux.intel.com,
 jithu.joseph@...el.com, kai.huang@...el.com, kan.liang@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
 ilpo.jarvinen@...ux.intel.com, peternewman@...gle.com,
 maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, eranian@...gle.com, james.morse@....com
Subject: Re: [PATCH v7 15/24] x86/resctrl: Implement resctrl_arch_assign_cntr
 to assign a counter with ABMC

Hi Reinette,

On 9/23/24 17:29, Reinette Chatre wrote:
> Hi Babu,
> 
> On 9/23/24 2:03 PM, Moger, Babu wrote:
>> Hi Reinette,
>>
>> On 9/19/24 12:13, Reinette Chatre wrote:
>>> Hi Babu,
>>>
>>> In subject, please use "()" for a function.
>>
>> Sure.
>>
>>>
>>> On 9/4/24 3:21 PM, Babu Moger wrote:
>>>> +/*
>>>> + * Send an IPI to the domain to assign the counter to RMID, event pair.
>>>> + */
>>>> +int resctrl_arch_assign_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
>>>> +			     enum resctrl_event_id evtid, u32 rmid, u32 closid,
>>>> +			     u32 cntr_id, bool assign)
>>>
>>> Looking ahead this is also called when config of existing assigned counter is
>>> changed. Should this thus perhaps be resctrl_arch_config_cntr()? 
>>
>> We have a matching resctrl_arch_assign_cntr() and
>> resctrl_arch_unassign_cntr() pair.
> 
> hmmm ... resctrl_arch_unassign_cntr() does not exist in this version of the series.

My bad. Confused with different versions.

Sure. Will change it resctrl_arch_config_cntr().


> 
>>
>> If we change resctrl_arch_config_cntr() then we need to change
>> resctrl_arch_unassign_cntr to resctrl_arch_unconfig_cntr().
>>
>> Should we change both?
>>
>>
>>>
>>>> +{
>>>> +	struct rdt_hw_mon_domain *hw_dom = resctrl_to_arch_mon_dom(d);
>>>> +	union l3_qos_abmc_cfg abmc_cfg = { 0 };
>>>> +	struct arch_mbm_state *arch_mbm;
>>>> +
>>>> +	abmc_cfg.split.cfg_en = 1;
>>>
>>> Just to confirm ... a counter remains "configured" from the hardware side whether it
>>> is assigned from resctrl perspective or not? It seems to me that once a counter is
>>> "unassigned" from resctrl perspective it needs no more context about that
>>> counter, yet it remains configured from hardware side?
>>
>> That is correct.
>> When unassigned, we are setting cntr_en = 0, so there is no counting. But
>> in hardware perspective it is still configured.
> 
> I think I misunderstood the "configured in hardware" to equate to "assigned by
> OS" when in fact it is just a bit to indicate when hardware makes changes
> requested by MSR write.
> 

That is correct. Hardware makes the changes only when cfg_en = 1.
Otherwise writing the MSR has no effect.
-- 
Thanks
Babu Moger