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

Moger, Babu
2025-04-14T20:51:18Z

Hi Reinette,

On 4/11/25 16:02, Reinette Chatre wrote:
> 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."

Sure.

>
>> + */
>> + 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.

Sure.

>
>> @@ -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.

How about?

"MBM Event configuration value representing reads, writes etc.."

>
>> + * @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.

Sure.

>
>> + */
>> +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.
>

Sure. Will check again.

--
Thanks
Babu Moger