linux-kernel - Re: [PATCH v7 05/24] x86/resctrl: Track the closid with the rmid

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Message-ID: <d0079d15-9950-5c74-75e9-aed848b48ea4@arm.com>
Date:   Wed, 13 Dec 2023 18:04:09 +0000
From:   James Morse <james.morse@....com>
To:     babu.moger@....com, x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        shameerali.kolothum.thodi@...wei.com,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        carl@...amperecomputing.com, lcherian@...vell.com,
        bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
        baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
        dfustini@...libre.com, amitsinght@...vell.com
Subject: Re: [PATCH v7 05/24] x86/resctrl: Track the closid with the rmid

Hi Babu,

On 09/11/2023 20:31, Moger, Babu wrote:
> On 10/25/23 13:03, James Morse wrote:
>> x86's RMID are independent of the CLOSID. An RMID can be allocated,
>> used and freed without considering the CLOSID.
>>
>> MPAM's equivalent feature is PMG, which is not an independent number,
>> it extends the CLOSID/PARTID space. For MPAM, only PMG-bits worth of
>> 'RMID' can be allocated for a single CLOSID.
>> i.e. if there is 1 bit of PMG space, then each CLOSID can have two
>> monitor groups.
>>
>> To allow resctrl to disambiguate RMID values for different CLOSID,
>> everything in resctrl that keeps an RMID value needs to know the CLOSID
>> too. This will always be ignored on x86.

>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 5d9864919f1c..2a0233cd0bc9 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -285,9 +300,9 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>>  		if (nrmid >= r->num_rmid)
>>  			break;
>>  
>> -		entry = __rmid_entry(nrmid);
>> +		entry = __rmid_entry(X86_RESCTRL_EMPTY_CLOSID, nrmid);// temporary
> 
> What is temporary means here? Can you please elaborate(or remove)?

It means this line gets removed in a subsequent patch - don't spend too long rationalising
the values used. This one gets removed in the next patch as __check_limbo() is changed to
operate by index instead.


Thanks,

James