linux-kernel - Re: [PATCH v3 07/21] x86/resctrl: Create mba_sc configuration in the rdt

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Date:   Wed, 30 Mar 2022 17:43:15 +0100
From:   James Morse <james.morse@....com>
To:     Reinette Chatre <reinette.chatre@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        shameerali.kolothum.thodi@...wei.com,
        Jamie Iles <jamie@...iainc.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        lcherian@...vell.com, bobo.shaobowang@...wei.com,
        tan.shaopeng@...itsu.com
Subject: Re: [PATCH v3 07/21] x86/resctrl: Create mba_sc configuration in the
 rdt_domain

Hi Reinette,

On 05/03/2022 00:26, Reinette Chatre wrote:
> On 2/17/2022 10:20 AM, James Morse wrote:
>> To support resctrl's MBA software controller, the architecture must provide
>> a second configuration array to hold the mbps_val[] from user-space.
>>
>> This complicates the interface between the architecture specific code and
>> the filesystem portions of resctrl that will move to /fs/, to allow
>> multiple architectures to support resctrl.
>>
>> Make the filesystem parts of resctrl create an array for the mba_sc
>> values when is_mba_sc() is set to true. The software controller
>> can be changed to use this, allowing the architecture code to only
>> consider the values configured in hardware.

...

>> @@ -3263,6 +3295,9 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
>>  		cancel_delayed_work(&d->cqm_limbo);
>>  	}
>>  
>> +	if (is_mba_sc(r))
>> +		mba_sc_domain_destroy(r, d);
>> +
>>  	domain_destroy_mon_state(d);
>>  }
>>  
>> @@ -3309,6 +3344,12 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
>>  	if (err)
>>  		return err;
>>  
>> +	err = mba_sc_domain_allocate(r, d);
>> +	if (err) {
>> +		domain_destroy_mon_state(d);
>> +		return err;
>> +	}
>> +

> Thank you for making this all symmetrical. It seems as though the new
> array is always created but only destroyed when is_mba_sc() is true.
> Is this correct?

That looks broken. Oops.

I'll fix it to always allocate the array, as that is what domain_setup_ctrlval() does
today, and it saves the hotplug headache.


Thanks,

James