Re: [PATCH v12 13/26] x86/resctrl: Implement resctrl_arch_config_cntr() to assign a counter with ABMC

Reinette Chatre
2025-04-11T21:02:49Z

Hi Babu,

On 4/3/25 5:18 PM, Babu Moger wrote:
> The ABMC feature provides an option to the user to assign a hardware
> counter to an RMID, event pair and monitor the bandwidth as long as it
> is assigned. The assigned RMID will be tracked by the hardware until the
> user unassigns it manually.
>
> Implement an architecture-specific handler to assign and unassign the
> counter. Configure counters by writing to the L3_QOS_ABMC_CFG MSR,
> specifying the counter ID, bandwidth source (RMID), and event
> configuration.
>
> 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).
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
...

> ---
> arch/x86/kernel/cpu/resctrl/monitor.c | 39 +++++++++++++++++++++++++++
> include/linux/resctrl.h | 15 +++++++++++
> 2 files changed, 54 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 8a88ac29d57d..77f8662dc50b 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -1430,3 +1430,42 @@ int resctrl_arch_mbm_cntr_assign_set(struct rdt_resource *r, bool enable)
>
> return 0;
> }
> +
> +static void resctrl_abmc_config_one_amd(void *info)
> +{
> + union l3_qos_abmc_cfg *abmc_cfg = info;
> +
> + wrmsrl(MSR_IA32_L3_QOS_ABMC_CFG, abmc_cfg->full);
> +}
> +
> +/*
> + * Send an IPI to the domain to assign the counter to RMID, event pair.
> + */
> +int resctrl_arch_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
> + enum resctrl_event_id evtid, u32 rmid, u32 closid,
> + u32 cntr_id, u32 evt_cfg, bool assign)
> +{
> + struct rdt_hw_mon_domain *hw_dom = resctrl_to_arch_mon_dom(d);
> + union l3_qos_abmc_cfg abmc_cfg = { 0 };
> + struct arch_mbm_state *am;
> +
> + abmc_cfg.split.cfg_en = 1;
> + abmc_cfg.split.cntr_en = assign ? 1 : 0;
> + abmc_cfg.split.cntr_id = cntr_id;
> + abmc_cfg.split.bw_src = rmid;
> + abmc_cfg.split.bw_type = evt_cfg;
> +
> + smp_call_function_any(&d->hdr.cpu_mask, resctrl_abmc_config_one_amd, &abmc_cfg, 1);
> +
> + /*
> + * Reset the architectural state so that reading of hardware
> + * counter is not considered as an overflow in next update.

Please add something like: "The hardware counter is reset (because cfg_en == 1)
so there is no need to record initial non-zero counts."

> + */
> + if (assign) {
> + am = get_arch_mbm_state(hw_dom, rmid, evtid);
> + if (am)
> + memset(am, 0, sizeof(*am));
> + }
> +
> + return 0;
> +}
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 294b15de664e..60270606f1b8 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h

Please keep the declaration internal to the arch code. It can be moved when
other architecture needs it.

> @@ -394,6 +394,21 @@ void resctrl_arch_mon_event_config_set(void *config_info);
> u32 resctrl_arch_mon_event_config_get(struct rdt_mon_domain *d,
> enum resctrl_event_id eventid);
>
> +/**
> + * resctrl_arch_config_cntr() - Configure the counter on the domain
> + * @r: resource that the counter should be read from.
> + * @d: domain that the counter should be read from.
> + * @evtid: event type to assign
> + * @rmid: rmid of the counter to read.
> + * @closid: closid that matches the rmid.
> + * @cntr_id: Counter ID to configure
> + * @evt_cfg: event configuration

"event configuration" is simply an expansion of member name and does not help to
understand what the value represents.

> + * @assign: assign or unassign

Please rework the kernel doc: consistent sentence structure (starts with upper case,
ends with period), use proper capitalization for acronyms (rmid -> RMID, etc.),
make descriptions informative.

> + */
> +int resctrl_arch_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
> + enum resctrl_event_id evtid, u32 rmid, u32 closid,
> + u32 cntr_id, u32 evt_cfg, bool assign);
> +
> /* For use by arch code to remap resctrl's smaller CDP CLOSID range */
> static inline u32 resctrl_get_config_index(u32 closid,
> enum resctrl_conf_type type)

This patch does not pass checkpatch.pl.

Reinette