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

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Message-ID: <4cce2fc9-2b42-4e10-b923-387611077d6b@arm.com>
Date: Fri, 16 Aug 2024 17:29:51 +0100
From: James Morse <james.morse@....com>
To: Babu Moger <babu.moger@....com>
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org,
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Subject: Re: [PATCH v6 09/22] x86/resctrl: Introduce MBM counters bitmap

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?


Thanks,

James