linux-kernel - Re: [RFC PATCH v3 08/17] x86/resctrl: Initialize assignable counters bitmap

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Date: Fri, 3 May 2024 16:31:23 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <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>,
	<yanjiewtw@...il.com>, <kim.phillips@....com>, <lukas.bulwahn@...il.com>,
	<seanjc@...gle.com>, <jmattson@...gle.com>, <leitao@...ian.org>,
	<jpoimboe@...nel.org>, <rick.p.edgecombe@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <jithu.joseph@...el.com>,
	<kai.huang@...el.com>, <kan.liang@...ux.intel.com>,
	<daniel.sneddon@...ux.intel.com>, <pbonzini@...hat.com>,
	<sandipan.das@....com>, <ilpo.jarvinen@...ux.intel.com>,
	<peternewman@...gle.com>, <maciej.wieczor-retman@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<eranian@...gle.com>, <james.morse@....com>
Subject: Re: [RFC PATCH v3 08/17] x86/resctrl: Initialize assignable counters
 bitmap

Hi Babu,

On 3/28/2024 6:06 PM, Babu Moger wrote:
> AMD Hardware provides a set of counters when the ABMC feature is supported.
> These counters are used for assigning events to the resctrl group.
> 
> Introduce the bitmap assign_cntrs_free_map to allocate and free the
> counters.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> 
> ---
> v3: Changed the bitmap name to assign_cntrs_free_map. Removed abmc
>     from the name.
> 
> v2: Changed the bitmap name to assignable_counter_free_map from
>     abmc_counter_free_map.
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index f49073c86884..2c7583e7b541 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -186,6 +186,22 @@ bool closid_allocated(unsigned int closid)
>  	return !test_bit(closid, &closid_free_map);
>  }
>  
> +static u64 assign_cntrs_free_map;
> +static u32 assign_cntrs_free_map_len;

Please provide summary in comments about what these globals are and how they
are used.

> +
> +static void assign_cntrs_init(void)
> +{
> +	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> +
> +	if (r->mbm_assign_cntrs > 64) {
> +		r->mbm_assign_cntrs = 64;
> +		WARN(1, "Cannot support more than 64 Assignable counters\n");

I am a bit confused here. The configuration registers are introduced in patch #10
and if I counted right there are 5 bits for the counter id. It thus seems to me
as though there needs to be some checking during enumeration time to ensure
that all counters enumerated can be configured.

> +	}
> +
> +	assign_cntrs_free_map = BIT_MASK(r->mbm_assign_cntrs) - 1;

Please use bitmap API. For example, bitmap_fill()

> +	assign_cntrs_free_map_len = r->mbm_assign_cntrs;
> +}
> +
>  /**
>   * rdtgroup_mode_by_closid - Return mode of resource group with closid
>   * @closid: closid if the resource group
> @@ -2459,6 +2475,9 @@ static int resctrl_abmc_setup(enum resctrl_res_level l, bool enable)
>  	struct rdt_resource *r = &rdt_resources_all[l].r_resctrl;
>  	struct rdt_domain *d;
>  
> +	/* Reset the counters bitmap */
> +	assign_cntrs_init();
> +

(At this point it is unclear when resctrl_abmc_setup() is called to understand
if reset of bitmap may be appropriate. Please do expand all changelogs to help
readers along with how this implementation is intended to work.)

>  	/* Update QOS_CFG MSR on all the CPUs in cpu_mask */
>  	list_for_each_entry(d, &r->domains, list) {
>  		on_each_cpu_mask(&d->cpu_mask, resctrl_abmc_msrwrite, &enable, 1);

Reinette