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

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Message-ID: <d6f2b7e1-21f1-4698-8c56-cb8e46374688@intel.com>
Date: Mon, 23 Sep 2024 15:29:33 -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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	<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 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.

> 
> 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.

Reinette