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

[Moger, Babu]

Hi Reinette,


On 5/3/24 18:32, Reinette Chatre wrote:
> 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?

Something like this in the changelog?

ABMC feature provides an option to assign(or pin) an RMID to the
hardware counter and monitor the bandwidth for a longer duration.

Hardware counters can be configured by writing to L3_QOS_ABMC_CFG MSR.
Configuration is done by setting the CfgEn field while specifying the
Bandwidth Source(RMID or CLOS), Bandwidth Types, and Counter Identifier.

Add the configuration register definition.

> 
>>
>> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
>> 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.

Sure.

> 
>> + */
>> +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"

Will change it to "reserved1" and "reserved" (below).

> 
> 
>> +			       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
> 

-- 
Thanks
Babu Moger