RE: [PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu

["Shaopeng Tan (Fujitsu)" <tan.shaopeng@fujitsu.com>]

Hi James,

> When a CPU is taken offline resctrl may need to move the overflow or limbo
> handlers to run on a different CPU.
> 
> Once the offline callbacks have been split, cqm_setup_limbo_handler() will be
> called while the CPU that is going offline is still present in the cpu_mask.
> 
> Pass the CPU to exclude to cqm_setup_limbo_handler() and
> mbm_setup_overflow_handler(). These functions can use a variant of
> cpumask_any_but() when selecting the CPU. -1 is used to indicate no CPUs
> need excluding.
> 
> A subsequent patch moves these calls to be before CPUs have been removed,
> so this exclude_cpus behaviour is temporary.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v2:
>  * Rephrased a comment to avoid a two letter bad-word. (we)
>  * Avoid assigning mbm_work_cpu if the domain is going to be free()d
>  * Added cpumask_any_housekeeping_but(), I dislike the name
> 
> Changes since v3:
>  * Marked an explanatory comment as temporary as the subsequent patch is
>    no longer adjacent.
> ---
>  arch/x86/kernel/cpu/resctrl/core.c     |  8 +++--
>  arch/x86/kernel/cpu/resctrl/internal.h | 37
> +++++++++++++++++++++--  arch/x86/kernel/cpu/resctrl/monitor.c
> | 42 +++++++++++++++++++++-----
> arch/x86/kernel/cpu/resctrl/rdtgroup.c |  6 ++--
>  include/linux/resctrl.h                |  3 ++
>  5 files changed, 82 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c
> b/arch/x86/kernel/cpu/resctrl/core.c
> index e00f3542e60e..187ed127a446 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -582,12 +582,16 @@ static void domain_remove_cpu(int cpu, struct
> rdt_resource *r)
>  	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);
> -			mbm_setup_overflow_handler(d, 0);
> +			/*
> +			 * 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(r, d)) {
>  			cancel_delayed_work(&d->cqm_limbo);
> -			cqm_setup_limbo_handler(d, 0);
> +			cqm_setup_limbo_handler(d, 0,
> RESCTRL_PICK_ANY_CPU);
>  		}
>  	}
>  }
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
> b/arch/x86/kernel/cpu/resctrl/internal.h
> index 021a8956518c..9cba8fc405b9 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -79,6 +79,37 @@ static inline unsigned int
> cpumask_any_housekeeping(const struct cpumask *mask)
>  	return cpu;
>  }
> 
> +/**
> + * cpumask_any_housekeeping_but() - Chose any cpu in @mask, preferring
> those
> + *			            that aren't marked nohz_full, excluding
> + *				    the provided CPU
> + * @mask:	The mask to pick a CPU from.
> + * @exclude_cpu:The CPU to avoid picking.
> + *
> + * Returns a CPU from @mask, but not @but. If there are housekeeping
> +CPUs that
> + * don't use nohz_full, these are preferred.
> + * Returns >= nr_cpu_ids if no CPUs are available.
> + */
> +static inline unsigned int
> +cpumask_any_housekeeping_but(const struct cpumask *mask, int
> +exclude_cpu) {
> +	int cpu, hk_cpu;
> +
> +	cpu = cpumask_any_but(mask, exclude_cpu);
> +	if (tick_nohz_full_cpu(cpu)) {
> +		hk_cpu = cpumask_nth_andnot(0, mask,
> tick_nohz_full_mask);
> +		if  (hk_cpu == exclude_cpu) {
> +			hk_cpu = cpumask_nth_andnot(1, mask,
> +						    tick_nohz_full_mask);
> +		}
> +
> +		if (hk_cpu < nr_cpu_ids)
> +			cpu = hk_cpu;
> +	}
> +
> +	return cpu;
> +}
> +
>  struct rdt_fs_context {
>  	struct kernfs_fs_context	kfc;
>  	bool				enable_cdpl2;
> @@ -564,11 +595,13 @@ void mon_event_read(struct rmid_read *rr, struct
> rdt_resource *r,
>  		    struct rdt_domain *d, struct rdtgroup *rdtgrp,
>  		    int evtid, int first);
>  void mbm_setup_overflow_handler(struct rdt_domain *dom,
> -				unsigned long delay_ms);
> +				unsigned long delay_ms,
> +				int exclude_cpu);
>  void mbm_handle_overflow(struct work_struct *work);  void __init
> intel_rdt_mbm_apply_quirk(void);  bool is_mba_sc(struct rdt_resource *r);
> -void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long
> delay_ms);
> +void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long
> delay_ms,
> +			     int exclude_cpu);
>  void cqm_handle_limbo(struct work_struct *work);  bool
> has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d);  void
> __check_limbo(struct rdt_domain *d, bool force_free); diff --git
> a/arch/x86/kernel/cpu/resctrl/monitor.c
> b/arch/x86/kernel/cpu/resctrl/monitor.c
> index ced933694f60..ae02185f3354 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -485,7 +485,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  		 * setup up the limbo worker.
>  		 */
>  		if (!has_busy_rmid(r, d))
> -			cqm_setup_limbo_handler(d,
> CQM_LIMBOCHECK_INTERVAL);
> +			cqm_setup_limbo_handler(d,
> CQM_LIMBOCHECK_INTERVAL, -1);
>  		set_bit(idx, d->rmid_busy_llc);
>  		entry->busy++;
>  	}
> @@ -810,15 +810,28 @@ void cqm_handle_limbo(struct work_struct *work)
>  	mutex_unlock(&rdtgroup_mutex);
>  }
> 
> -void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long
> delay_ms)
> +/**
> + * cqm_setup_limbo_handler() - Schedule the limbo handler to run for this
> + *                             domain.
> + * @delay_ms:      How far in the future the handler should run.
> + * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any
> CPU.
> + */
> +void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long
> delay_ms,
> +			     int exclude_cpu)
>  {
>  	unsigned long delay = msecs_to_jiffies(delay_ms);
>  	int cpu;
> 
> -	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> -	dom->cqm_work_cpu = cpu;
> +	if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
> +		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> +	else
> +		cpu = cpumask_any_housekeeping_but(&dom->cpu_mask,
> +						   exclude_cpu);
> 
> -	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
> +	if (cpu < nr_cpu_ids) {
> +		dom->cqm_work_cpu = cpu;
> +		schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
> +	}
>  }
> 
>  void mbm_handle_overflow(struct work_struct *work) @@ -864,7 +877,14
> @@ void mbm_handle_overflow(struct work_struct *work)
>  	mutex_unlock(&rdtgroup_mutex);
>  }
> 
> -void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long
> delay_ms)
> +/**
> + * mbm_setup_overflow_handler() - Schedule the overflow handler to run for
> this
> + *                                domain.
> + * @delay_ms:      How far in the future the handler should run.
> + * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any
> CPU.
> + */
> +void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long
> delay_ms,
> +				int exclude_cpu)
>  {
>  	unsigned long delay = msecs_to_jiffies(delay_ms);
>  	int cpu;
> @@ -875,9 +895,15 @@ void mbm_setup_overflow_handler(struct rdt_domain
> *dom, unsigned long delay_ms)
>  	 */
>  	if (!resctrl_mounted || !resctrl_arch_mon_capable())
>  		return;
> -	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> +	if (exclude_cpu == -1)
> +		cpu = cpumask_any_housekeeping(&dom->cpu_mask);

Should RESCTRL_PICK_ANY_CPU be used instead of -1?

Best regards,
Shaopeng TAN