Re: [PATCH v4 13/19] x86/resctrl: Add data structures for ABMC assignment

Reinette Chatre
2024-06-14T01:45:09Z

Hi Babu,

On 5/24/24 5:23 AM, Babu Moger wrote:
> The ABMC feature provides an option to the user to assign a hardware
> counter to an RMID and monitor the bandwidth as long as the counter
> is assigned. The bandwidth events will be tracked by the hardware until
> the user changes the configuration. Each resctrl group can configure
> maximum two counters, one for total event and one for local event.
>
> The counters are configured by writing to MSR L3_QOS_ABMC_CFG.
> Configuration is done by setting the counter id, bandwidth source (RMID),
> bandwidth types. Reading L3_QOS_ABMC_DSC returns the configuration of

What is a "bandwidth type" here?

> the counter id specified in L3_QOS_ABMC_CFG.
>
> Attempts to read or write these MSRs when ABMC is not enabled will result
> in a #GP(0) exception.
>
> MSR L3_QOS_ABMC_CFG (0xC000_03FDh) and L3_QOS_ABMC_DSC (0xC000_03FEh)
> details.
> ==========================================================================
> 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
> ==========================================================================
>

This is copy&paste from AMD spec but needs some translation to map it to
resctrl.

> The feature details are documented 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).
>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
> ---
> v4: Added more descriptions.
> Changed the name abmc_ctr_id to ctr_id.
> Added L3_QOS_ABMC_DSC. Used for reading the configuration.
>
> v3: No changes.
>
> v2: No changes.
> ---
> arch/x86/include/asm/msr-index.h | 2 ++
> arch/x86/kernel/cpu/resctrl/internal.h | 30 ++++++++++++++++++++++++++
> 2 files changed, 32 insertions(+)
>
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 5f9a0139e98c..6d2fe39ac68f 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -1172,6 +1172,8 @@
> #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
> +#define MSR_IA32_L3_QOS_ABMC_DSC 0xc00003fe
>
> /* 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 60a1ca0a11a7..45ed33f4f0ff 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -107,6 +107,9 @@ cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
> #define ASSIGN_TOTAL BIT(QOS_L3_MBM_TOTAL_EVENT_ID)
> #define ASSIGN_LOCAL BIT(QOS_L3_MBM_LOCAL_EVENT_ID)
>
> +/* Maximum assignable counters per resctrl group */
> +#define MAX_CNTRS 2
> +
> struct rdt_fs_context {
> struct kernfs_fs_context kfc;
> bool enable_cdpl2;
> @@ -211,6 +214,7 @@ enum rdtgrp_mode {
> * @crdtgrp_list: child rdtgroup node list
> * @rmid: rmid for this rdtgroup
> * @mon_state: Assignment state of the group
> + * @ctr_id: ABMC counter ids assigned to this group
> */
> struct mongroup {
> struct kernfs_node *mon_data_kn;
> @@ -218,6 +222,7 @@ struct mongroup {
> struct list_head crdtgrp_list;
> u32 rmid;
> u32 mon_state;
> + u32 ctr_id[MAX_CNTRS];

To match "num_cntrs" it seems "cntr_id" may be more appropriate?

> };
>
> /**
> @@ -568,6 +573,31 @@ union cpuid_0x10_x_edx {
> unsigned int full;
> };
>
> +/*
> + * ABMC counters can be configured by writing to L3_QOS_ABMC_CFG.

extra space

> + * @bw_type : Bandwidth types to track for this counter

What is a "Bandwidth type"? What are possible values?

> + * @bw_src : Bandwidth Source (RMID or CLOSID)
> + * @reserved1 : Reserved
> + * @is_cos : BwSrc field is a COS (not an RMID)

Please be consistent wrt "CLOS"/"CLOSID" in comment and member name

> + * @ctr_id : Counter Identifier

Please be consistent with "cntr" vs "ctr". Earlier the series
introduces "num_cntrs" so cntr seems appropriate?

> + * @reserved : Reserved
> + * @ctr_en : Counter Enable bit
> + * @cfg_en : Configuration Enable bit

Why are there two enable bits? How are they used?

(please match other kernel doc wrt : usage)

> + */
> +union l3_qos_abmc_cfg {
> + struct {
> + unsigned long bw_type :32,
> + bw_src :12,
> + reserved1: 3,
> + is_cos : 1,
> + ctr_id : 5,
> + reserved : 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