Re: [RFC PATCH v3 08/17] x86/resctrl: Initialize assignable counters bitmap

Reinette Chatre
2024-05-03T23:31:32Z

Hi Babu,

On 3/28/2024 6:06 PM, Babu Moger wrote:
> AMD Hardware provides a set of counters when the ABMC feature is supported.
> These counters are used for assigning events to the resctrl group.
>
> Introduce the bitmap assign_cntrs_free_map to allocate and free the
> counters.
>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
>
> ---
> v3: Changed the bitmap name to assign_cntrs_free_map. Removed abmc
> from the name.
>
> v2: Changed the bitmap name to assignable_counter_free_map from
> abmc_counter_free_map.
> ---
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index f49073c86884..2c7583e7b541 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -186,6 +186,22 @@ bool closid_allocated(unsigned int closid)
> return !test_bit(closid, &closid_free_map);
> }
>
> +static u64 assign_cntrs_free_map;
> +static u32 assign_cntrs_free_map_len;

Please provide summary in comments about what these globals are and how they
are used.

> +
> +static void assign_cntrs_init(void)
> +{
> + struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> +
> + if (r->mbm_assign_cntrs > 64) {
> + r->mbm_assign_cntrs = 64;
> + WARN(1, "Cannot support more than 64 Assignable counters\n");

I am a bit confused here. The configuration registers are introduced in patch #10
and if I counted right there are 5 bits for the counter id. It thus seems to me
as though there needs to be some checking during enumeration time to ensure
that all counters enumerated can be configured.

> + }
> +
> + assign_cntrs_free_map = BIT_MASK(r->mbm_assign_cntrs) - 1;

Please use bitmap API. For example, bitmap_fill()

> + assign_cntrs_free_map_len = r->mbm_assign_cntrs;
> +}
> +
> /**
> * rdtgroup_mode_by_closid - Return mode of resource group with closid
> * @closid: closid if the resource group
> @@ -2459,6 +2475,9 @@ static int resctrl_abmc_setup(enum resctrl_res_level l, bool enable)
> struct rdt_resource *r = &rdt_resources_all[l].r_resctrl;
> struct rdt_domain *d;
>
> + /* Reset the counters bitmap */
> + assign_cntrs_init();
> +

(At this point it is unclear when resctrl_abmc_setup() is called to understand
if reset of bitmap may be appropriate. Please do expand all changelogs to help
readers along with how this implementation is intended to work.)

> /* Update QOS_CFG MSR on all the CPUs in cpu_mask */
> list_for_each_entry(d, &r->domains, list) {
> on_each_cpu_mask(&d->cpu_mask, resctrl_abmc_msrwrite, &enable, 1);

Reinette