linux-kernel - Re: [PATCH v6 15/22] x86/resctrl: Add the interface to assign a hardware counter

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Message-ID: <63bdd436-7bc3-4ccb-a182-5ae596fefd5a@arm.com>
Date: Fri, 16 Aug 2024 17:30:25 +0100
From: James Morse <james.morse@....com>
To: Babu Moger <babu.moger@....com>
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org,
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Subject: Re: [PATCH v6 15/22] x86/resctrl: Add the interface to assign a
 hardware counter

Hi Babu,

On 06/08/2024 23:00, 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 it is assigned.
> The assigned RMID will be tracked by the hardware until the user unassigns
> it manually.
> 
> Counters are configured by writing to L3_QOS_ABMC_CFG MSR and
> specifying the counter id, bandwidth source, and bandwidth types.
> 
> Provide the interface to assign the counter ids to RMID.
> 
> 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).


> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 60696b248b56..1ee91a7293a8 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1864,6 +1864,103 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,

> +/*
> + * Send an IPI to the domain to assign the counter id to RMID.
> + */
> +int resctrl_arch_assign_cntr(struct rdt_mon_domain *d, enum resctrl_event_id evtid,
> +			     u32 rmid, u32 cntr_id, u32 closid, bool assign)

MPAM ends up with a per-resource array of monitor-ids that it uses to map cntr_id
allocated by resctrl to the underlying hardware id. Could this function pass the struct
rdt_resource too?
(this saves me having to assume its the L3 - adding to the technical debt in this area)

Nit: could closid and rmid appear next to each other, and in that order ... just to fit
with other helpers that take both.


> +{
> +	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 *arch_mbm;
> +
> +	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;
> +
> +	/* Update the event configuration from the domain */
> +	if (evtid == QOS_L3_MBM_TOTAL_EVENT_ID) {
> +		abmc_cfg.split.bw_type = hw_dom->mbm_total_cfg;
> +		arch_mbm = &hw_dom->arch_mbm_total[rmid];
> +	} else {
> +		abmc_cfg.split.bw_type = hw_dom->mbm_local_cfg;
> +		arch_mbm = &hw_dom->arch_mbm_local[rmid];
> +	}
> +
> +	smp_call_function_any(&d->hdr.cpu_mask, rdtgroup_abmc_cfg, &abmc_cfg, 1);
> +
> +	/*
> +	 * Reset the architectural state so that reading of hardware
> +	 * counter is not considered as an overflow in next update.
> +	 */
> +	if (arch_mbm)
> +		memset(arch_mbm, 0, sizeof(struct arch_mbm_state));
> +
> +	return 0;
> +}


Thanks,

James