Re: [RFC PATCH v3 07/17] x86/resctrl: Add support to enable/disable ABMC feature

Peter Newman
2024-04-04T00:31:05Z

Hi Babu,

On Thu, Mar 28, 2024 at 6:07 PM Babu Moger <babu.moger@amd.com> wrote:
> struct rdt_fs_context {
> struct kernfs_fs_context kfc;
> bool enable_cdpl2;
> @@ -433,6 +436,7 @@ struct rdt_parse_data {
> * @mbm_cfg_mask: Bandwidth sources that can be tracked when Bandwidth
> * Monitoring Event Configuration (BMEC) is supported.
> * @cdp_enabled: CDP state of this resource
> + * @abmc_enabled: ABMC feature is enabled
> *
> * Members of this structure are either private to the architecture
> * e.g. mbm_width, or accessed via helpers that provide abstraction. e.g.
> @@ -448,6 +452,7 @@ struct rdt_hw_resource {
> unsigned int mbm_width;
> unsigned int mbm_cfg_mask;
> bool cdp_enabled;
> + bool abmc_enabled;
> };
>
> static inline struct rdt_hw_resource *resctrl_to_arch_res(struct rdt_resource *r)
> @@ -491,6 +496,13 @@ static inline bool resctrl_arch_get_cdp_enabled(enum resctrl_res_level l)
>
> int resctrl_arch_set_cdp_enabled(enum resctrl_res_level l, bool enable);
>
> +static inline bool resctrl_arch_get_abmc_enabled(enum resctrl_res_level l)
> +{
> + return rdt_resources_all[l].abmc_enabled;
> +}

This inline definition will not work in either this file or
fs/resctrl/internal.h, following James's change[1] moving the code.

resctrl_arch-definitions are either declared in linux/resctrl.h or
defined inline in a file like asm/resctrl.h.

> +
> +int resctrl_arch_set_abmc_enabled(enum resctrl_res_level l, bool enable);
> +
> /*
> * To return the common struct rdt_resource, which is contained in struct
> * rdt_hw_resource, walk the resctrl member of struct rdt_hw_resource.
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 05f551bc316e..f49073c86884 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -850,9 +850,15 @@ static int rdtgroup_mbm_assign_show(struct kernfs_open_file *of,
> struct seq_file *s, void *v)
> {
> struct rdt_resource *r = of->kn->parent->priv;
> + struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>
> - if (r->mbm_assign_capable)
> + if (r->mbm_assign_capable && hw_res->abmc_enabled) {
> + seq_puts(s, "[abmc]\n");
> + seq_puts(s, "legacy_mbm\n");
> + } else if (r->mbm_assign_capable) {
> seq_puts(s, "abmc\n");
> + seq_puts(s, "[legacy_mbm]\n");
> + }

This looks like it would move to fs/resctrl/rdtgroup.c where it's not
possible to dereference an rdt_hw_resource struct.

It might be helpful to try building your changes on top of James's
change[1] to get an idea of how this would fit in post-refactoring.
I'll stop pointing out inconsistencies with his portability scheme
now.

>
> return 0;
> }
> @@ -2433,6 +2439,74 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level l, bool enable)
> return 0;
> }
>
> +static void resctrl_abmc_msrwrite(void *arg)
> +{
> + bool *enable = arg;
> + u64 msrval;
> +
> + rdmsrl(MSR_IA32_L3_QOS_EXT_CFG, msrval);
> +
> + if (*enable)
> + msrval |= ABMC_ENABLE;
> + else
> + msrval &= ~ABMC_ENABLE;
> +
> + wrmsrl(MSR_IA32_L3_QOS_EXT_CFG, msrval);
> +}
> +
> +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;
> +
> + /* 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);
> + resctrl_arch_reset_rmid_all(r, d);
> + }
> +
> + return 0;
> +}
> +
> +static int resctrl_abmc_enable(enum resctrl_res_level l)
> +{
> + struct rdt_hw_resource *hw_res = &rdt_resources_all[l];
> + int ret = 0;
> +
> + if (!hw_res->abmc_enabled) {
> + ret = resctrl_abmc_setup(l, true);
> + if (!ret)
> + hw_res->abmc_enabled = true;

Presumably this would be called holding the rdtgroup_mutex? Perhaps a
lockdep assertion somewhere would be appropriate?

Thanks!
-Peter

[1] https://lore.kernel.org/lkml/20240321165106.31602-32-james.morse@arm.com/