Re: [PATCH v7 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu

[Moger, Babu]

On 10/25/23 13:03, James Morse wrote:
> 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@xxxxxxxxxxx>
> Tested-by: Peter Newman <peternewman@xxxxxxxxxx>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>

Reviewed-by: Babu Moger <babu.moger@xxxxxxx>

> ---
> 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.
> 
> Changes since v4:
>  * Check against RESCTRL_PICK_ANY_CPU instead of -1.
>  * Leave cqm_work_cpu as nr_cpu_ids when no CPU is available.
>  * Made cpumask_any_housekeeping_but() more readable.
> 
> Changes since v5:
>  * Changes in captialisation, and a typo.
>  * Merged cpumask helpers.
> 
> Changes since v6:
>  * Added the missing dom parameter to some kernel doc.
>  * Re-added use of cpumask_any_but(),
>  * Expanded comment above cpumask_any_housekeeping(),
>  * Added some more comments for good measure.
>  * Added explicit IS_ENABLED() check as gcc-12 doesn't seem to work this out.
> ---
>  arch/x86/kernel/cpu/resctrl/core.c        |  8 +++--
>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  2 +-
>  arch/x86/kernel/cpu/resctrl/internal.h    | 33 ++++++++++++++----
>  arch/x86/kernel/cpu/resctrl/monitor.c     | 42 ++++++++++++++++++-----
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c    |  6 ++--
>  include/linux/resctrl.h                   |  2 ++
>  6 files changed, 72 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 1a74e9c47416..7e44f2c40897 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -586,12 +586,16 @@ 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(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/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index a033e8e32108..64db51455df3 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -552,7 +552,7 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>  		return;
>  	}
>  
> -	cpu = cpumask_any_housekeeping(&d->cpu_mask);
> +	cpu = cpumask_any_housekeeping(&d->cpu_mask, RESCTRL_PICK_ANY_CPU);
>  
>  	/*
>  	 * cpumask_any_housekeeping() prefers housekeeping CPUs, but
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index c4c1e1909058..f5fff2f0d866 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -61,19 +61,36 @@
>   * cpumask_any_housekeeping() - Choose any CPU in @mask, preferring those that
>   *			        aren't marked nohz_full
>   * @mask:	The mask to pick a CPU from.
> + * @exclude_cpu:The CPU to avoid picking.
>   *
> - * Returns a CPU in @mask. If there are housekeeping CPUs that don't use
> - * nohz_full, these are preferred.
> + * Returns a CPU from @mask, but not @exclude_cpu. If there are housekeeping
> + * CPUs that don't use nohz_full, these are preferred. Pass
> + * RESCTRL_PICK_ANY_CPU to avoid excluding any CPUs.
> + *
> + * When a CPU is excluded, returns >= nr_cpu_ids if no CPUs are available.
>   */
> -static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask)
> +static inline unsigned int
> +cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
>  {
>  	unsigned int cpu, hk_cpu;
>  
> -	cpu = cpumask_any(mask);
> -	if (!tick_nohz_full_cpu(cpu))
> +	if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
> +		cpu = cpumask_any(mask);
> +	else
> +		cpu = cpumask_any_but(mask, exclude_cpu);
> +
> +	if (!IS_ENABLED(CONFIG_NO_HZ_FULL))
> +		return cpu;
> +
> +	/* If the CPU picked isn't marked nohz_full, we're done */
> +	if (cpu <= nr_cpu_ids && !tick_nohz_full_cpu(cpu))
>  		return cpu;
>  
> +	/* Try to find a CPU that isn't nohz_full to use in preference */
>  	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;
>  
> @@ -575,11 +592,13 @@ 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_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 87379d2a339c..241b3dd8646c 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -481,7 +481,8 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  		 * setup up the limbo worker.
>  		 */
>  		if (!has_busy_rmid(d))
> -			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL);
> +			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL,
> +						RESCTRL_PICK_ANY_CPU);
>  		set_bit(idx, d->rmid_busy_llc);
>  		entry->busy++;
>  	}
> @@ -808,7 +809,8 @@ void cqm_handle_limbo(struct work_struct *work)
>  	__check_limbo(d, false);
>  
>  	if (has_busy_rmid(d)) {
> -		d->cqm_work_cpu = cpumask_any_housekeeping(&d->cpu_mask);
> +		d->cqm_work_cpu = cpumask_any_housekeeping(&d->cpu_mask,
> +							   RESCTRL_PICK_ANY_CPU);
>  		schedule_delayed_work_on(d->cqm_work_cpu, &d->cqm_limbo,
>  					 delay);
>  	}
> @@ -816,15 +818,25 @@ 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.
> + * @dom:           The domain the limbo handler should run for.
> + * @delay_ms:      How far in the future the handler should run.
> + * @exclude_cpu:   Which CPU the handler should not run on,
> + *		   RESCTRL_PICK_ANY_CPU 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);
> +	cpu = cpumask_any_housekeeping(&dom->cpu_mask, exclude_cpu);
>  	dom->cqm_work_cpu = cpu;
>  
> -	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
> +	if (cpu < nr_cpu_ids)
> +		schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
>  }
>  
>  void mbm_handle_overflow(struct work_struct *work)
> @@ -862,14 +874,24 @@ void mbm_handle_overflow(struct work_struct *work)
>  	 * Re-check for housekeeping CPUs. This allows the overflow handler to
>  	 * move off a nohz_full CPU quickly.
>  	 */
> -	d->mbm_work_cpu = cpumask_any_housekeeping(&d->cpu_mask);
> +	d->mbm_work_cpu = cpumask_any_housekeeping(&d->cpu_mask,
> +						   RESCTRL_PICK_ANY_CPU);
>  	schedule_delayed_work_on(d->mbm_work_cpu, &d->mbm_over, delay);
>  
>  out_unlock:
>  	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.
> + * @dom:           The domain the overflow handler should run for.
> + * @delay_ms:      How far in the future the handler should run.
> + * @exclude_cpu:   Which CPU the handler should not run on,
> + *		   RESCTRL_PICK_ANY_CPU 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;
> @@ -880,9 +902,11 @@ 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);
> +	cpu = cpumask_any_housekeeping(&dom->cpu_mask, exclude_cpu);
>  	dom->mbm_work_cpu = cpu;
> -	schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
> +
> +	if (cpu < nr_cpu_ids)
> +		schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
>  }
>  
>  static int dom_data_init(struct rdt_resource *r)
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index ab9db7ce706f..e22e0f6adeb3 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -2683,7 +2683,8 @@ static int rdt_get_tree(struct fs_context *fc)
>  	if (is_mbm_enabled()) {
>  		r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>  		list_for_each_entry(dom, &r->domains, list)
> -			mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL);
> +			mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL,
> +						   RESCTRL_PICK_ANY_CPU);
>  	}
>  
>  	goto out;
> @@ -3994,7 +3995,8 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
>  
>  	if (is_mbm_enabled()) {
>  		INIT_DELAYED_WORK(&d->mbm_over, mbm_handle_overflow);
> -		mbm_setup_overflow_handler(d, MBM_OVERFLOW_INTERVAL);
> +		mbm_setup_overflow_handler(d, MBM_OVERFLOW_INTERVAL,
> +					   RESCTRL_PICK_ANY_CPU);
>  	}
>  
>  	if (is_llc_occupancy_enabled())
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 4c4bad3c34e4..ccbbbe5d18d3 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -10,6 +10,8 @@
>  #define RESCTRL_RESERVED_CLOSID		0
>  #define RESCTRL_RESERVED_RMID		0
>  
> +#define RESCTRL_PICK_ANY_CPU		-1
> +
>  #ifdef CONFIG_PROC_CPU_RESCTRL
>  
>  int proc_resctrl_show(struct seq_file *m,

-- 
Thanks
Babu Moger