Re: [RFC PATCH v3 10/17] x86/resctrl: Add data structures for ABMC assignment

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Babu,

On 3/28/2024 6:06 PM, Babu Moger wrote:
> ABMC (Bandwidth Monitoring Event Configuration) counters can be configured
> by writing to L3_QOS_ABMC_CFG MSR. When ABMC is enabled, the user can
> configure a counter by writing to L3_QOS_ABMC_CFG setting the CfgEn field
> while specifying the Bandwidth Source, Bandwidth Types, and Counter
> Identifier. Add the MSR definition and individual field definitions.
> 
> MSR L3_QOS_ABMC_CFG (C000_03FDh) definitions.
> 
> ==========================================================================
> Bits 	Mnemonic	Description		Access Type   Reset Value
> ==========================================================================
> 63 	CfgEn 		Configuration Enable 	R/W 		0
> 
> 62 	CtrEn 		Counter Enable 		R/W 		0
> 
> 61:53 	– 		Reserved 		MBZ 		0
> 
> 52:48 	CtrID 		Counter Identifier	R/W		0
> 
> 47 	IsCOS		BwSrc field is a COS	R/W		0
> 			(not an RMID)
> 
> 46:44 	–		Reserved		MBZ		0
> 
> 43:32	BwSrc		Bandwidth Source	R/W		0
> 			(RMID or COS)
> 
> 31:0	BwType		Bandwidth types to	R/W		0
> 			track for this counter
> ==========================================================================
> 
> The feature details are documentd in the 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).

This changelog is purely a summary of the hardware architecture. I have not come
across a clear explanation on how this architecture is intended to be supported
by resctrl. When would resctrl need/want to set particular fields? What is
the mapping to resctrl?

> 
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
> 
> ---
> v3: No changes.
> v2: No changes.
> ---
>  arch/x86/include/asm/msr-index.h       |  1 +
>  arch/x86/kernel/cpu/resctrl/internal.h | 23 +++++++++++++++++++++++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index f16ee50b1a23..ab01abfab089 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -1166,6 +1166,7 @@
>  #define MSR_IA32_SMBA_BW_BASE		0xc0000280
>  #define MSR_IA32_EVT_CFG_BASE		0xc0000400
>  #define MSR_IA32_L3_QOS_EXT_CFG		0xc00003ff
> +#define MSR_IA32_L3_QOS_ABMC_CFG	0xc00003fd
>  
>  /* MSR_IA32_VMX_MISC bits */
>  #define MSR_IA32_VMX_MISC_INTEL_PT                 (1ULL << 14)
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index b559b3a4555e..41b06d46ea74 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -106,6 +106,9 @@ cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
>  #define ASSIGN_TOTAL			BIT(0)
>  #define ASSIGN_LOCAL			BIT(1)
>  
> +/* Maximum assignable counters per resctrl group */
> +#define MAX_ASSIGN_CNTRS		2
> +
>  struct rdt_fs_context {
>  	struct kernfs_fs_context	kfc;
>  	bool				enable_cdpl2;
> @@ -210,6 +213,7 @@ enum rdtgrp_mode {
>   * @crdtgrp_list:		child rdtgroup node list
>   * @rmid:			rmid for this rdtgroup
>   * @mon_state:			Assignment state of the group
> + * @abmc_ctr_id:		ABMC counterids assigned to this group
>   */
>  struct mongroup {
>  	struct kernfs_node	*mon_data_kn;
> @@ -217,6 +221,7 @@ struct mongroup {
>  	struct list_head	crdtgrp_list;
>  	u32			rmid;
>  	u32			mon_state;
> +	u32			abmc_ctr_id[MAX_ASSIGN_CNTRS];
>  };
>  
>  /**
> @@ -566,6 +571,24 @@ union cpuid_0x10_x_edx {
>  	unsigned int full;
>  };
>  
> +/*
> + * L3_QOS_ABMC_CFG MSR details. ABMC counters can be configured
> + * by writing to L3_QOS_ABMC_CFG.

There are many fields in this structure ... how is resctrl expected
to set these fields in order to configure a counter? Please expand the
comments.

> + */
> +union l3_qos_abmc_cfg {
> +	struct {
> +		unsigned long  bw_type	:32,
> +			       bw_src	:12,
> +			       rsvrd1	: 3,

Considering how "reserved" is spelled it is
unexpected to see "rsvrd"


> +			       is_cos	: 1,
> +			       ctr_id	: 5,
> +			       rsvrd	: 9,
> +			       ctr_en	: 1,
> +			       cfg_en	: 1;
> +	} split;
> +	unsigned long full;
> +};
> +
>  void rdt_last_cmd_clear(void);
>  void rdt_last_cmd_puts(const char *s);
>  __printf(1, 2)


Reinette