Re: [RFC PATCH v3 12/17] x86/resctrl: Add the functionality to assign the RMID

Reinette Chatre
2024-05-03T23:34:05Z

Hi Babu,

On 3/28/2024 6:06 PM, Babu Moger wrote:
> With the support of ABMC (Assignable Bandwidth Monitoring Counters)
> feature, the user has the option to assign or unassign the RMID to
> hardware counter and monitor the bandwidth for the longer duration.

What is meant with "the longer duration" (this term is used throughout
this series)? Perhaps "for as long as a hardware counter is assigned"?

>
> Provide the interface to assign the counter to the group.
>
> The ABMC feature implements a pair of MSRs, L3_QOS_ABMC_CFG (MSR
> C000_03FDh) and L3_QOS_ABMC_DSC (MSR C000_3FEh). Each logical processor
> implements a separate copy of these registers. Attempts to read or write
> these MSRs when ABMC is not enabled will result in a #GP(0) exception.
>
> Individual assignable bandwidth counters are configured by writing to
> L3_QOS_ABMC_CFG MSR and specifying the Counter ID, Bandwidth Source, and
> Bandwidth Types. Reading L3_QOS_ABMC_DSC returns the configuration of the
> counter specified by L3_QOS_ABMC_CFG [CtrID].

This mentions the AMD architecture parts needing configuration but not what
resctrl parts are used to accomplish this configuration. It is difficult to
understand this work without this connection.

>
> 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
> ---
> v3: Removed the static from the prototype of rdtgroup_assign_abmc.
> The function is not called directly from user anymore. These
> changes are related to global assignment interface.
>
> v2: Minor text changes in commit message.
> ---
> arch/x86/kernel/cpu/resctrl/internal.h | 1 +
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 86 ++++++++++++++++++++++++++
> 2 files changed, 87 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 88453c86474b..9d84c80104f9 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -651,6 +651,7 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
> void __init resctrl_file_fflags_init(const char *config,
> unsigned long fflags);
> void arch_domain_mbm_evt_config(struct rdt_hw_domain *hw_dom);
> +ssize_t rdtgroup_assign_abmc(struct rdtgroup *rdtgrp, u32 evtid, int mon_state);
> void rdt_staged_configs_clear(void);
> bool closid_allocated(unsigned int closid);
> int resctrl_find_cleanest_closid(void);
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 7f54788a58de..cfbdaf8b5f83 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -202,6 +202,18 @@ static void assign_cntrs_init(void)
> assign_cntrs_free_map_len = r->mbm_assign_cntrs;
> }
>
> +static int assign_cntrs_alloc(void)
> +{
> + u32 counterid = ffs(assign_cntrs_free_map);
> +
> + if (counterid == 0)
> + return -ENOSPC;
> + counterid--;
> + assign_cntrs_free_map &= ~(1 << counterid);
> +
> + return counterid;

Use bitmap API ... eg. find_first_bit() (eliminates
need to adjust counterid), __clear_bit()

> +}
> +
> /**
> * rdtgroup_mode_by_closid - Return mode of resource group with closid
> * @closid: closid if the resource group
> @@ -1848,6 +1860,80 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
> return ret ?: nbytes;
> }
>
> +static void rdtgroup_abmc_msrwrite(void *info)
> +{
> + u64 *msrval = info;
> +
> + wrmsrl(MSR_IA32_L3_QOS_ABMC_CFG, *msrval);
> +}
> +
> +static void rdtgroup_abmc_domain(struct rdt_domain *d, struct rdtgroup *rdtgrp,
> + u32 evtid, int index, bool assign)
> +{
> + struct rdt_hw_domain *hw_dom = resctrl_to_arch_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.ctr_en = assign ? 1 : 0;
> + abmc_cfg.split.ctr_id = rdtgrp->mon.abmc_ctr_id[index];
> + abmc_cfg.split.bw_src = rdtgrp->mon.rmid;
> +
> + /*
> + * Read the event configuration from the domain and pass it as
> + * bw_type.
> + */
> + 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[rdtgrp->mon.rmid];
> + } else {
> + abmc_cfg.split.bw_type = hw_dom->mbm_local_cfg;
> + arch_mbm = &hw_dom->arch_mbm_local[rdtgrp->mon.rmid];
> + }
> +
> + smp_call_function_any(&d->cpu_mask, rdtgroup_abmc_msrwrite, &abmc_cfg, 1);
> +
> + /* Reset the internal counters */
> + if (arch_mbm)
> + memset(arch_mbm, 0, sizeof(struct arch_mbm_state));
> +}
> +
> +ssize_t rdtgroup_assign_abmc(struct rdtgroup *rdtgrp, u32 evtid, int mon_state)
> +{
> + struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> + int counterid = 0, index;
> + struct rdt_domain *d;
> +
> + if (rdtgrp->mon.mon_state & mon_state) {
> + rdt_last_cmd_puts("ABMC counter is assigned already\n");
> + return 0;
> + }
> +
> + index = mon_event_config_index_get(evtid);
> + if (index == INVALID_CONFIG_INDEX) {
> + pr_warn_once("Invalid event id %d\n", evtid);
> + return -EINVAL;
> + }
> +
> + /*
> + * Allocate a new counter and update domains
> + */
> + counterid = assign_cntrs_alloc();
> + if (counterid < 0) {
> + rdt_last_cmd_puts("Out of ABMC counters\n");
> + return -ENOSPC;
> + }
> +
> + rdtgrp->mon.abmc_ctr_id[index] = counterid;
> +
> + list_for_each_entry(d, &r->domains, list)
> + rdtgroup_abmc_domain(d, rdtgrp, evtid, index, 1);
> +
> + rdtgrp->mon.mon_state |= mon_state;
> +
> + return 0;
> +}
> +
> /* rdtgroup information files for one cache resource. */
> static struct rftype res_common_files[] = {
> {

It is not clear to me where the filesystem and architecture boundaries
are, but I understand that you and Peter already discussed this and I look
forward to next version that will make this easier to understand.

Reinette