Re: [PATCH v3 07/21] x86/resctrl: Create mba_sc configuration in the rdt_domain

From: Reinette Chatre
Date: Fri Mar 04 2022 - 19:26:27 EST


Hi James,

On 2/17/2022 10:20 AM, James Morse wrote:
> To support resctrl's MBA software controller, the architecture must provide
> a second configuration array to hold the mbps_val[] from user-space.
>
> This complicates the interface between the architecture specific code and
> the filesystem portions of resctrl that will move to /fs/, to allow
> multiple architectures to support resctrl.
>
> Make the filesystem parts of resctrl create an array for the mba_sc
> values when is_mba_sc() is set to true. The software controller
> can be changed to use this, allowing the architecture code to only
> consider the values configured in hardware.
>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> ---
> Changes since v2:
> * Split patch in two, the liftime parts are a separate patch.
> * Added reset in set_mba_sc() now that we can't depend on the lifetime.
> * Initialise ret in mba_sc_allocate(),
> * Made mbps_val allocation/freeing symmetric for cpuhp calls.
> * Removed reference to squashed-out struct.
> * Preserved kerneldoc for mbps_val.
>
> Changes since v1:
> * Added missing error handling to mba_sc_domain_allocate() in
> domain_setup_mon_state()
> * Added comment about mba_sc_domain_allocate() races
> * Squashed out struct resctrl_mba_sc
> * Moved mount time alloc/free calls to set_mba_sc().
> * Removed mount check in resctrl_offline_domain()
> * Reword commit message
> ---
> arch/x86/kernel/cpu/resctrl/internal.h | 1 -
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 41 ++++++++++++++++++++++++++
> include/linux/resctrl.h | 7 +++++
> 3 files changed, 48 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index e12b55f815bf..a7e2cbce29d5 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -36,7 +36,6 @@
> #define MBM_OVERFLOW_INTERVAL 1000
> #define MAX_MBA_BW 100u
> #define MBA_IS_LINEAR 0x4
> -#define MBA_MAX_MBPS U32_MAX
> #define MAX_MBA_BW_AMD 0x800
> #define MBM_CNTR_WIDTH_OFFSET_AMD 20
>
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 794a84ba9097..e4313f907eb6 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1889,6 +1889,30 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r)
> l3_qos_cfg_update(&hw_res->cdp_enabled);
> }
>
> +static int mba_sc_domain_allocate(struct rdt_resource *r, struct rdt_domain *d)
> +{
> + u32 num_closid = resctrl_arch_get_num_closid(r);
> + int cpu = cpumask_any(&d->cpu_mask);
> + int i;
> +
> + d->mbps_val = kcalloc_node(num_closid, sizeof(*d->mbps_val),
> + GFP_KERNEL, cpu_to_node(cpu));
> + if (!d->mbps_val)
> + return -ENOMEM;
> +
> + for (i = 0; i < num_closid; i++)
> + d->mbps_val[i] = MBA_MAX_MBPS;
> +
> + return 0;
> +}
> +
> +static void mba_sc_domain_destroy(struct rdt_resource *r,
> + struct rdt_domain *d)
> +{
> + kfree(d->mbps_val);
> + d->mbps_val = NULL;
> +}
> +


...

> @@ -3263,6 +3295,9 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
> cancel_delayed_work(&d->cqm_limbo);
> }
>
> + if (is_mba_sc(r))
> + mba_sc_domain_destroy(r, d);
> +
> domain_destroy_mon_state(d);
> }
>
> @@ -3309,6 +3344,12 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
> if (err)
> return err;
>
> + err = mba_sc_domain_allocate(r, d);
> + if (err) {
> + domain_destroy_mon_state(d);
> + return err;
> + }
> +

Thank you for making this all symmetrical. It seems as though the new
array is always created but only destroyed when is_mba_sc() is true.
Is this correct?

Reinette