Re: [PATCH v5 23/24] x86/resctrl: Move domain helper migration into resctrl_offline_cpu()

[Reinette Chatre]

Hi James,

On 7/28/2023 9:42 AM, James Morse wrote:
> When a CPU is taken offline the resctrl filesystem code needs to check
> if it was the CPU nominated to perform the periodic overflow and limbo
> work. If so, another CPU needs to be chosen to do this work.
> 
> This is currently done in core.c, mixed in with the code that removes
> the CPU from the domain's mask, and potentially free()s the domain.
> 
> Move the migration of the overflow and limbo helpers into the filesystem
> code, into resctrl_offline_cpu(). As resctrl_offline_cpu() runs before
> the architecture code has removed the CPU from the domain mask, the
> callers need to be told which CPU is being removed, to avoid picking
> it as the new CPU. This uses the exclude_cpu feature previously
> added.
> 
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> ---
>  arch/x86/kernel/cpu/resctrl/core.c     | 16 ----------------
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 15 +++++++++++++++
>  2 files changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 6eb9408a942a..edc0dd123317 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -578,22 +578,6 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
>  
>  		return;
>  	}
> -
> -	if (r == &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl) {
> -		if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
> -			cancel_delayed_work(&d->mbm_over);
> -			/*
> -			 * temporary: exclude_cpu=-1 as this CPU has already
> -			 * been removed by cpumask_clear_cpu()d
> -			 */
> -			mbm_setup_overflow_handler(d, 0, RESCTRL_PICK_ANY_CPU);
> -		}
> -		if (is_llc_occupancy_enabled() && cpu == d->cqm_work_cpu &&
> -		    has_busy_rmid(d)) {
> -			cancel_delayed_work(&d->cqm_limbo);
> -			cqm_setup_limbo_handler(d, 0, RESCTRL_PICK_ANY_CPU);
> -		}
> -	}
>  }
>  
>  static void clear_closid_rmid(int cpu)
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 12a628b5d476..a256a96df487 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -3892,7 +3892,9 @@ static void clear_childcpus(struct rdtgroup *r, unsigned int cpu)
>  
>  void resctrl_offline_cpu(unsigned int cpu)
>  {
> +	struct rdt_domain *d;
>  	struct rdtgroup *rdtgrp;
> +	struct rdt_resource *l3 = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;

Please always keep reverse fir order.

>  
>  	lockdep_assert_held(&rdtgroup_mutex);
>  
> @@ -3902,6 +3904,19 @@ void resctrl_offline_cpu(unsigned int cpu)
>  			break;
>  		}
>  	}
> +

Can there be a l3->mon_capable check here to make things clear?

> +	d = get_domain_from_cpu(cpu, l3);
> +	if (d) {
> +		if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
> +			cancel_delayed_work(&d->mbm_over);
> +			mbm_setup_overflow_handler(d, 0, cpu);
> +		}
> +		if (is_llc_occupancy_enabled() && cpu == d->cqm_work_cpu &&
> +		    has_busy_rmid(d)) {
> +			cancel_delayed_work(&d->cqm_limbo);
> +			cqm_setup_limbo_handler(d, 0, cpu);
> +		}
> +	}
>  }
>  
>  /*

Reinette