RE: [PATCH v4 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read()

[Shaopeng Tan (Fujitsu)]

Hello James,


> Depending on the number of monitors available, Arm's MPAM may need to
> allocate a monitor prior to reading the counter value. Allocating a contended
> resource may involve sleeping.
> 
> add_rmid_to_limbo() calls resctrl_arch_rmid_read() for multiple domains, the
> allocation should be valid for all domains.
> 
> __check_limbo() and mon_event_count() each make multiple calls to
> resctrl_arch_rmid_read(), to avoid extra work on contended systems, the
> allocation should be valid for multiple invocations of resctrl_arch_rmid_read().
> 
> Add arch hooks for this allocation, which need calling before
> resctrl_arch_rmid_read(). The allocated monitor is passed to
> resctrl_arch_rmid_read(), then freed again afterwards. The helper can be
> called on any CPU, and can sleep.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> ----
> Changes since v3:
>  * Expanded comment.
>  * Removed stray header include.
>  * Reworded commit message.
>  * Made ctx a void * instead of an int.
> ---
>  arch/x86/include/asm/resctrl.h            | 11 ++++++++++
>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  5 +++++
>  arch/x86/kernel/cpu/resctrl/internal.h    |  1 +
>  arch/x86/kernel/cpu/resctrl/monitor.c     | 26
> +++++++++++++++++++----
>  include/linux/resctrl.h                   |  5 ++++-
>  5 files changed, 43 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index 78376c19ee6f..20729364982b 100644
> --- a/arch/x86/include/asm/resctrl.h
> +++ b/arch/x86/include/asm/resctrl.h
> @@ -136,6 +136,17 @@ static inline u32 resctrl_arch_rmid_idx_encode(u32
> ignored, u32 rmid)
>  	return rmid;
>  }
> 
> +/* x86 can always read an rmid, nothing needs allocating */ struct
> +rdt_resource; static inline void *resctrl_arch_mon_ctx_alloc(struct
> +rdt_resource *r, int evtid) {
> +	might_sleep();
> +	return NULL;
> +};
> +
> +static inline void resctrl_arch_mon_ctx_free(struct rdt_resource *r, int evtid,
> +					     void *ctx) { };
> +
>  void resctrl_cpu_detect(struct cpuinfo_x86 *c);
> 
>  #else
> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index 6eeccad192ee..280d66fae21c 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -546,6 +546,9 @@ void mon_event_read(struct rmid_read *rr, struct
> rdt_resource *r,
>  	rr->d = d;
>  	rr->val = 0;
>  	rr->first = first;
> +	rr->arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, evtid);
> +	if (IS_ERR(rr->arch_mon_ctx))
> +		return;
> 
>  	cpu = cpumask_any_housekeeping(&d->cpu_mask);
> 
> @@ -559,6 +562,8 @@ void mon_event_read(struct rmid_read *rr, struct
> rdt_resource *r,
>  		smp_call_function_any(&d->cpu_mask, mon_event_count, rr,
> 1);
>  	else
>  		smp_call_on_cpu(cpu, smp_mon_event_count, rr, false);
> +
> +	resctrl_arch_mon_ctx_free(r, evtid, rr->arch_mon_ctx);
>  }
> 
>  int rdtgroup_mondata_show(struct seq_file *m, void *arg) diff --git
> a/arch/x86/kernel/cpu/resctrl/internal.h
> b/arch/x86/kernel/cpu/resctrl/internal.h
> index 7960366b9434..a7e025cffdbc 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -136,6 +136,7 @@ struct rmid_read {
>  	bool			first;
>  	int			err;
>  	u64			val;
> +	void			*arch_mon_ctx;
>  };
> 
>  extern bool rdt_alloc_capable;
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> b/arch/x86/kernel/cpu/resctrl/monitor.c
> index fb33100e172b..6d140018358a 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -264,7 +264,7 @@ static u64 mbm_overflow_count(u64 prev_msr, u64
> cur_msr, unsigned int width)
> 
>  int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
>  			   u32 closid, u32 rmid, enum resctrl_event_id
> eventid,
> -			   u64 *val)
> +			   u64 *val, void *ignored)
>  {
>  	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>  	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d); @@
> -331,9 +331,14 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>  	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>  	struct rmid_entry *entry;
>  	u32 idx, cur_idx = 1;
> +	void *arch_mon_ctx;
>  	bool rmid_dirty;
>  	u64 val = 0;
> 
> +	arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r,
> QOS_L3_OCCUP_EVENT_ID);
> +	if (arch_mon_ctx < 0)
> +		return;
> +

Would it be better to use IS_ERR() macro?

>  	/*
>  	 * Skip RMID 0 and start from RMID 1 and check all the RMIDs that
>  	 * are marked as busy for occupancy < threshold. If the occupancy @@
> -347,7 +352,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
> 
>  		entry = __rmid_entry(idx);
>  		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
> -					   QOS_L3_OCCUP_EVENT_ID,
> &val)) {
> +					   QOS_L3_OCCUP_EVENT_ID,
> &val,
> +					   arch_mon_ctx)) {
>  			rmid_dirty = true;
>  		} else {
>  			rmid_dirty = (val >= resctrl_rmid_realloc_threshold);
> @@ -360,6 +366,8 @@ void __check_limbo(struct rdt_domain *d, bool
> force_free)
>  		}
>  		cur_idx = idx + 1;
>  	}
> +
> +	resctrl_arch_mon_ctx_free(r, QOS_L3_OCCUP_EVENT_ID,
> arch_mon_ctx);
>  }
> 
>  bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d) @@ -539,7
> +547,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct
> rmid_read *rr)
>  	}
> 
>  	rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid, rr->evtid,
> -					 &tval);
> +					 &tval, rr->arch_mon_ctx);
>  	if (rr->err)
>  		return rr->err;
> 
> @@ -589,7 +597,6 @@ void mon_event_count(void *info)
>  	int ret;
> 
>  	rdtgrp = rr->rgrp;
> -
>  	ret = __mon_event_count(rdtgrp->closid, rdtgrp->mon.rmid, rr);
> 
>  	/*
> @@ -749,11 +756,21 @@ static void mbm_update(struct rdt_resource *r, struct
> rdt_domain *d,
>  	if (is_mbm_total_enabled()) {
>  		rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
>  		rr.val = 0;
> +		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> +		if (rr.arch_mon_ctx < 0)
> +			return;
> +
Same here.

>  		__mon_event_count(closid, rmid, &rr);
> +
> +		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
>  	}
>  	if (is_mbm_local_enabled()) {
>  		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
>  		rr.val = 0;
> +		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> +		if (rr.arch_mon_ctx < 0)
> +			return;
> +
Same here.

Best regards,
Shaopeng TAN