Re: [PATCH v2 04/17] x86/resctrl: Detect Assignable Bandwidth Monitoring feature details

[James Morse]

Hi Babu,

On 19/01/2024 18:22, Babu Moger wrote:
> ABMC feature details are reported via CPUID Fn8000_0020_EBX_x5.
> Bits Description
> 15:0 MAX_ABMC Maximum Supported Assignable Bandwidth
>      Monitoring Counter ID + 1
> 
> Detect the feature details and update
> /sys/fs/resctrl/info/L3_MON/mon_features.
> 
> If the system supports Assignable Bandwidth Monitoring Counters (ABMC),
> the output will have additional text.
>  $ cat /sys/fs/resctrl/info/L3_MON/mon_features
>    mbm_assign_capable
> 
> The feature details are documented in APM listed below [1].
> [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming
> Publication # 24593 Revision 3.41 section 19.3.3.3 Assignable Bandwidth
> Monitoring (ABMC).

> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 4efe2d6a9eb7..f40ee271a5c7 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -303,6 +303,17 @@ static void rdt_get_cdp_l2_config(void)
>  	rdt_get_cdp_config(RDT_RESOURCE_L2);
>  }
>  
> +static void rdt_get_abmc_cfg(struct rdt_resource *r)
> +{
> +	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
> +	u32 eax, ebx, ecx, edx;
> +
> +	r->mbm_assign_capable = true;
> +	/* Query CPUID_Fn80000020_EBX_x05 for number of ABMC counters */
> +	cpuid_count(0x80000020, 5, &eax, &ebx, &ecx, &edx);

> +	hw_res->mbm_assignable_counters = (ebx & 0xFFFF) + 1;

Please put the mbm_assignable_counters field in struct rdt_resource. The filesystem code
needs to access this to allocate/free counters and report how many are available.
After all this gets split and the filesystem code moves to /fs/, the rdt_hw_resrouce
structure is inaccessible to the filesystem code.


> +}
> +
>  static void
>  mba_wrmsr_amd(struct rdt_domain *d, struct msr_param *m, struct rdt_resource *r)
>  {
> @@ -815,6 +826,12 @@ static __init bool get_rdt_alloc_resources(void)
>  	if (get_slow_mem_config())
>  		ret = true;
>  
> +	if (rdt_cpu_has(X86_FEATURE_ABMC)) {
> +		r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> +		rdt_get_abmc_cfg(r);

> +		ret = true;

Does it make sense to report rdt_alloc_capable if the SoC has ABMC, but nothing that can
be configured?

This code would probably make more sense in the get_rdt_mon_resources().


> +	}
> +
>  	return ret;
>  }
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index a4f1aa15f0a2..01eb0522b42b 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -391,6 +391,8 @@ struct rdt_parse_data {
>   *			resctrl_arch_get_num_closid() to avoid confusion
>   *			with struct resctrl_schema's property of the same name,
>   *			which has been corrected for features like CDP.

> + * @mbm_assignable_counters:
> + *			Maximum number of assignable ABMC counters

As above, please move this to struct rdt_resource. The 'hw' version becomes private to the
arch code after the move to /fs//


>   * @msr_base:		Base MSR address for CBMs
>   * @msr_update:		Function pointer to update QOS MSRs
>   * @mon_scale:		cqm counter * mon_scale = occupancy in bytes


Thanks,

James