Re: [PATCH v6 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read()

["Moger, Babu" <bmoger@amd.com>]

Hi James,

On 9/14/2023 12:21 PM, James Morse wrote:
> 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.
>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Tested-By: Peter Newman <peternewman@google.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v3:
>   * Expanded comment.
>   * Removed stray header include.
>   * Reworded commit message.
>   * Made ctx a void * instead of an int.
>
> Changes since v4:
>   * Used IS_ERR() in more places.
>
> Changes since v5:
>   * Pass the error back from mon_event_read() as -EINVAL/Unavailable.
>   * Add some ratelimited warnings when failing to allocate a mon context
> ---
>   arch/x86/include/asm/resctrl.h            | 11 ++++++++
>   arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  7 +++++
>   arch/x86/kernel/cpu/resctrl/internal.h    |  1 +
>   arch/x86/kernel/cpu/resctrl/monitor.c     | 34 +++++++++++++++++++++--
>   include/linux/resctrl.h                   |  5 +++-
>   5 files changed, 54 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index 1d274dbabc44..29c4cc343787 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 bd263b9a0abd..ce4821ea111b 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -546,6 +546,11 @@ 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)) {
> +		rr->err = -EINVAL;
> +		return;
> +	}
>   
>   	cpu = cpumask_any_housekeeping(&d->cpu_mask);
>   
> @@ -559,6 +564,8 @@ 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 37bb3de37a4a..66d9ebb5e03a 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 05d949ec94f1..28a2c8765faf 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -270,7 +270,7 @@ 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 unused, 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);
> @@ -325,9 +325,17 @@ 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 (IS_ERR(arch_mon_ctx)) {
> +		pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> +				    PTR_ERR(arch_mon_ctx));
> +		return;
> +	}
> +
>   	/*
>   	 * Skip RMID 0 and start from RMID 1 and check all the RMIDs that
>   	 * are marked as busy for occupancy < threshold. If the occupancy
> @@ -341,7 +349,8 @@ 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);
> @@ -354,6 +363,8 @@ 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_domain *d)
> @@ -532,7 +543,7 @@ 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;
>   
> @@ -743,11 +754,27 @@ 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 (IS_ERR(rr.arch_mon_ctx)) {
> +			pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> +					    PTR_ERR(rr.arch_mon_ctx));
> +			return;
> +		}
> +
>   		__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 (IS_ERR(rr.arch_mon_ctx)) {
> +			pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> +					    PTR_ERR(rr.arch_mon_ctx));
> +			return;
> +		}
> +
>   		__mon_event_count(closid, rmid, &rr);
>   
>   		/*
> @@ -757,6 +784,7 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d,
>   		 */
>   		if (is_mba_sc(NULL))
>   			mbm_bw_count(closid, rmid, &rr);
> +		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);

Space before the last line would be cleaner.

                 if (is_mba_sc(NULL))
  			mbm_bw_count(closid, rmid, &rr);
+
+		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);


>   	}
>   }
>   
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index f7311102e94c..5e4b4df9610b 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -235,6 +235,9 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
>    * @rmid:		rmid of the counter to read.
>    * @eventid:		eventid to read, e.g. L3 occupancy.
>    * @val:		result of the counter read in bytes.
> + * @arch_mon_ctx:	An architecture specific value from
> + *			resctrl_arch_mon_ctx_alloc(), for MPAM this identifies
> + *			the hardware monitor allocated for this read request.
>    *
>    * Some architectures need to sleep when first programming some of the counters.
>    * (specifically: arm64's MPAM cache occupancy counters can return 'not ready'
> @@ -248,7 +251,7 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
>    */
>   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 *arch_mon_ctx);

Just wondering.. Have you thought about passing rmid_read structure to 
this function?

Because most of the information is already inside the rmid_read 
structure. We can avoid passing 7 parameters.

Thanks

Babu

>   
>   /**
>    * resctrl_arch_rmid_read_context_check()  - warn about invalid contexts