linux-kernel - Re: [PATCH v6 09/22] x86/resctrl: Introduce MBM counters bitmap

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Message-ID: <5310acf5-0d6b-475b-a2e3-8071757d1735@amd.com>
Date: Fri, 16 Aug 2024 15:39:15 -0500
From: "Moger, Babu" <babu.moger@....com>
To: James Morse <james.morse@....com>
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Subject: Re: [PATCH v6 09/22] x86/resctrl: Introduce MBM counters bitmap

Hi James,

On 8/16/24 11:29, James Morse wrote:
> Hi Babu,
> 
> On 06/08/2024 23:00, Babu Moger wrote:
>> Hardware provides a set of counters when mbm_cntr_assignable feature is
>> supported. These counters are used for assigning the events in resctrl
>> group when the feature is enabled.
>>
>> Introduce mbm_cntrs_free_map bitmap to track available and free counters
>> and set of routines to allocate and free the counters.
> 
> 
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index ab4fab3b7cf1..c818965e36c9 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -185,6 +185,37 @@ bool closid_allocated(unsigned int closid)
>>  	return !test_bit(closid, &closid_free_map);
>>  }
>>  
>> +/*
>> + * Counter bitmap for tracking the available counters.
>> + * ABMC feature provides set of hardware counters for enabling events.
>> + * Each event takes one hardware counter. Kernel needs to keep track
>> + * of number of available counters.
>> + */
>> +static DECLARE_BITMAP(mbm_cntrs_free_map, 64);
> 
> Please make this resctrl limit of '64' a define in linux/resctrl.h so the arch code knows
> what the limit is!
> 
> MPAM platforms may have more than this - and really bad things happen if mbm_cntrs_init()
> passes bitmap_fill() a value greater than 64.
> 
> Even better - could we dynamically allocate this bitmap using the size advertised by the
> architecture code?

Yes. Actually, I was thinking about allocating it dynamically. It needs
few other changes as well. Will do it.

-- 
Thanks
Babu Moger