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

[Reinette Chatre <reinette.chatre@intel.com>]

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@arm.com>
> ---
> 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