Message-ID: <a0afaae6-0b7c-4a94-9b2a-b09c8016922a@nvidia.com>
Date: Fri, 3 Oct 2025 09:54:53 -0700
From: Fenghua Yu <fenghuay@...dia.com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
 Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 baisheng.gao@...soc.com, Jonathan Cameron <jonathan.cameron@...wei.com>,
 Rob Herring <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>, Ben Horgan <ben.horgan@....com>
Subject: Re: [PATCH v2 08/29] arm_mpam: Add the class and component structures
 for firmware described ris

Hi, James,

On 9/10/25 13:42, James Morse wrote:
> An MSC is a container of resources, each identified by their RIS index.
> Some RIS are described by firmware to provide their position in the system.
> Others are discovered when the driver probes the hardware.
>
> To configure a resource it needs to be found by its class, e.g. 'L2'.
> There are two kinds of grouping, a class is a set of components, which
> are visible to user-space as there are likely to be multiple instances
> of the L2 cache. (e.g. one per cluster or package)
>
> Add support for creating and destroying structures to allow a hierarchy
> of resources to be created.
>
> CC: Ben Horgan <ben.horgan@....com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v1:
>   * Fixed a comp/vmsc typo.
>   * Removed duplicate description from the commit message.
>   * Moved parenthesis in the add_to_garbage() macro.
>   * Check for out of range ris_idx when creating ris.
>   * Removed GFP as probe_lock is no longer a spin lock.
>   * Removed alloc flag as ended up searching the lists itself.
>   * Added a comment about affinity masks not overlapping.
>
> Changes since RFC:
>   * removed a pr_err() debug message that crept in.
> ---
>   drivers/resctrl/mpam_devices.c  | 406 +++++++++++++++++++++++++++++++-
>   drivers/resctrl/mpam_internal.h |  90 +++++++
>   include/linux/arm_mpam.h        |   8 +-
>   3 files changed, 493 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index efc4738e3b4d..c7f4981b3545 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -18,7 +18,6 @@
>   #include <linux/printk.h>
>   #include <linux/slab.h>
>   #include <linux/spinlock.h>
> -#include <linux/srcu.h>
>   #include <linux/types.h>
>   
>   #include "mpam_internal.h"
> @@ -31,7 +30,7 @@
>   static DEFINE_MUTEX(mpam_list_lock);
>   static LIST_HEAD(mpam_all_msc);
>   
> -static struct srcu_struct mpam_srcu;
> +struct srcu_struct mpam_srcu;
>   
>   /*
>    * Number of MSCs that have been probed. Once all MSC have been probed MPAM
> @@ -39,6 +38,402 @@ static struct srcu_struct mpam_srcu;
>    */
>   static atomic_t mpam_num_msc;
>   
> +/*
> + * An MSC is a physical container for controls and monitors, each identified by
> + * their RIS index. These share a base-address, interrupts and some MMIO
> + * registers. A vMSC is a virtual container for RIS in an MSC that control or
> + * monitor the same thing. Members of a vMSC are all RIS in the same MSC, but
> + * not all RIS in an MSC share a vMSC.
> + * Components are a group of vMSC that control or monitor the same thing but
> + * are from different MSC, so have different base-address, interrupts etc.
> + * Classes are the set components of the same type.
> + *
> + * The features of a vMSC is the union of the RIS it contains.
> + * The features of a Class and Component are the common subset of the vMSC
> + * they contain.
> + *
> + * e.g. The system cache may have bandwidth controls on multiple interfaces,
> + * for regulating traffic from devices independently of traffic from CPUs.
> + * If these are two RIS in one MSC, they will be treated as controlling
> + * different things, and will not share a vMSC/component/class.
> + *
> + * e.g. The L2 may have one MSC and two RIS, one for cache-controls another
> + * for bandwidth. These two RIS are members of the same vMSC.
> + *
> + * e.g. The set of RIS that make up the L2 are grouped as a component. These
> + * are sometimes termed slices. They should be configured the same, as if there
> + * were only one.
> + *
> + * e.g. The SoC probably has more than one L2, each attached to a distinct set
> + * of CPUs. All the L2 components are grouped as a class.
> + *
> + * When creating an MSC, struct mpam_msc is added to the all mpam_all_msc list,
> + * then linked via struct mpam_ris to a vmsc, component and class.
> + * The same MSC may exist under different class->component->vmsc paths, but the
> + * RIS index will be unique.
> + */
> +LIST_HEAD(mpam_classes);
> +
> +/* List of all objects that can be free()d after synchronise_srcu() */
> +static LLIST_HEAD(mpam_garbage);
> +
> +#define init_garbage(x)	init_llist_node(&(x)->garbage.llist)
> +
> +static struct mpam_vmsc *
> +mpam_vmsc_alloc(struct mpam_component *comp, struct mpam_msc *msc)
> +{
> +	struct mpam_vmsc *vmsc;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	vmsc = kzalloc(sizeof(*vmsc), GFP_KERNEL);
> +	if (!vmsc)
> +		return ERR_PTR(-ENOMEM);
> +	init_garbage(vmsc);
> +
> +	INIT_LIST_HEAD_RCU(&vmsc->ris);
> +	INIT_LIST_HEAD_RCU(&vmsc->comp_list);
> +	vmsc->comp = comp;
> +	vmsc->msc = msc;
> +
> +	list_add_rcu(&vmsc->comp_list, &comp->vmsc);
> +
> +	return vmsc;
> +}
> +
> +static struct mpam_vmsc *mpam_vmsc_get(struct mpam_component *comp,
> +				       struct mpam_msc *msc)
> +{
> +	struct mpam_vmsc *vmsc;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	list_for_each_entry(vmsc, &comp->vmsc, comp_list) {
> +		if (vmsc->msc->id == msc->id)
> +			return vmsc;
> +	}
> +
> +	return mpam_vmsc_alloc(comp, msc);
> +}
> +
> +static struct mpam_component *
> +mpam_component_alloc(struct mpam_class *class, int id)
> +{
> +	struct mpam_component *comp;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	comp = kzalloc(sizeof(*comp), GFP_KERNEL);
> +	if (!comp)
> +		return ERR_PTR(-ENOMEM);
> +	init_garbage(comp);
> +
> +	comp->comp_id = id;
> +	INIT_LIST_HEAD_RCU(&comp->vmsc);
> +	/* affinity is updated when ris are added */
> +	INIT_LIST_HEAD_RCU(&comp->class_list);
> +	comp->class = class;
> +
> +	list_add_rcu(&comp->class_list, &class->components);
> +
> +	return comp;
> +}
> +
> +static struct mpam_component *
> +mpam_component_get(struct mpam_class *class, int id)
> +{
> +	struct mpam_component *comp;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	list_for_each_entry(comp, &class->components, class_list) {
> +		if (comp->comp_id == id)
> +			return comp;
> +	}
> +
> +	return mpam_component_alloc(class, id);
> +}
> +
> +static struct mpam_class *
> +mpam_class_alloc(u8 level_idx, enum mpam_class_types type)
> +{
> +	struct mpam_class *class;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	class = kzalloc(sizeof(*class), GFP_KERNEL);
> +	if (!class)
> +		return ERR_PTR(-ENOMEM);
> +	init_garbage(class);
> +
> +	INIT_LIST_HEAD_RCU(&class->components);
> +	/* affinity is updated when ris are added */
> +	class->level = level_idx;
> +	class->type = type;
> +	INIT_LIST_HEAD_RCU(&class->classes_list);
> +
> +	list_add_rcu(&class->classes_list, &mpam_classes);
> +
> +	return class;
> +}
> +
> +static struct mpam_class *
> +mpam_class_get(u8 level_idx, enum mpam_class_types type)
> +{
> +	bool found = false;
> +	struct mpam_class *class;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	list_for_each_entry(class, &mpam_classes, classes_list) {
> +		if (class->type == type && class->level == level_idx) {
> +			found = true;
> +			break;
> +		}
> +	}
> +
> +	if (found)
> +		return class;
> +
> +	return mpam_class_alloc(level_idx, type);
> +}
> +
> +#define add_to_garbage(x)				\
> +do {							\
> +	__typeof__(x) _x = (x);				\
> +	_x->garbage.to_free = _x;			\
> +	llist_add(&_x->garbage.llist, &mpam_garbage);	\
> +} while (0)
> +
> +static void mpam_class_destroy(struct mpam_class *class)
> +{
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	list_del_rcu(&class->classes_list);
> +	add_to_garbage(class);
> +}
> +
> +static void mpam_comp_destroy(struct mpam_component *comp)
> +{
> +	struct mpam_class *class = comp->class;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	list_del_rcu(&comp->class_list);
> +	add_to_garbage(comp);
> +
> +	if (list_empty(&class->components))
> +		mpam_class_destroy(class);
> +}
> +
> +static void mpam_vmsc_destroy(struct mpam_vmsc *vmsc)
> +{
> +	struct mpam_component *comp = vmsc->comp;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	list_del_rcu(&vmsc->comp_list);
> +	add_to_garbage(vmsc);
> +
> +	if (list_empty(&comp->vmsc))
> +		mpam_comp_destroy(comp);
> +}
> +
> +static void mpam_ris_destroy(struct mpam_msc_ris *ris)
> +{
> +	struct mpam_vmsc *vmsc = ris->vmsc;
> +	struct mpam_msc *msc = vmsc->msc;
> +	struct platform_device *pdev = msc->pdev;
> +	struct mpam_component *comp = vmsc->comp;
> +	struct mpam_class *class = comp->class;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	/*
> +	 * It is assumed affinities don't overlap. If they do the class becomes
> +	 * unusable immediately.
> +	 */
> +	cpumask_andnot(&comp->affinity, &comp->affinity, &ris->affinity);
> +	cpumask_andnot(&class->affinity, &class->affinity, &ris->affinity);
> +	clear_bit(ris->ris_idx, &msc->ris_idxs);
> +	list_del_rcu(&ris->vmsc_list);
> +	list_del_rcu(&ris->msc_list);
> +	add_to_garbage(ris);
> +	ris->garbage.pdev = pdev;
> +
> +	if (list_empty(&vmsc->ris))
> +		mpam_vmsc_destroy(vmsc);
> +}
> +
> +/*
> + * There are two ways of reaching a struct mpam_msc_ris. Via the
> + * class->component->vmsc->ris, or via the msc.
> + * When destroying the msc, the other side needs unlinking and cleaning up too.
> + */
> +static void mpam_msc_destroy(struct mpam_msc *msc)
> +{
> +	struct platform_device *pdev = msc->pdev;
> +	struct mpam_msc_ris *ris, *tmp;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	list_for_each_entry_safe(ris, tmp, &msc->ris, msc_list)
> +		mpam_ris_destroy(ris);
> +
> +	list_del_rcu(&msc->all_msc_list);
> +	platform_set_drvdata(pdev, NULL);
> +
> +	add_to_garbage(msc);
> +	msc->garbage.pdev = pdev;
> +}
> +
> +static void mpam_free_garbage(void)
> +{
> +	struct mpam_garbage *iter, *tmp;
> +	struct llist_node *to_free = llist_del_all(&mpam_garbage);
> +

Should this be protected by mpam_list_lock and check if the lock is held?

+	lockdep_assert_held(&mpam_list_lock);

Multiple threads may add and free garbage in parallel. Please see later free_garbage() is not protected by any lock.

> +	if (!to_free)
> +		return;
> +
> +	synchronize_srcu(&mpam_srcu);
> +
> +	llist_for_each_entry_safe(iter, tmp, to_free, llist) {
> +		if (iter->pdev)
> +			devm_kfree(&iter->pdev->dev, iter->to_free);
> +		else
> +			kfree(iter->to_free);
> +	}
> +}
> +
> +/*
> + * The cacheinfo structures are only populated when CPUs are online.
> + */
> +int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
> +				   cpumask_t *affinity)
> +{
> +	return acpi_pptt_get_cpumask_from_cache_id(cache_id, affinity);
> +}
> +
> +/*
> + * cpumask_of_node() only knows about online CPUs. This can't tell us whether
> + * a class is represented on all possible CPUs.
> + */
> +static void get_cpumask_from_node_id(u32 node_id, cpumask_t *affinity)
> +{
> +	int cpu;
> +
> +	for_each_possible_cpu(cpu) {
> +		if (node_id == cpu_to_node(cpu))
> +			cpumask_set_cpu(cpu, affinity);
> +	}
> +}
> +
> +static int mpam_ris_get_affinity(struct mpam_msc *msc, cpumask_t *affinity,
> +				 enum mpam_class_types type,
> +				 struct mpam_class *class,
> +				 struct mpam_component *comp)
> +{
> +	int err;
> +
> +	switch (type) {
> +	case MPAM_CLASS_CACHE:
> +		err = mpam_get_cpumask_from_cache_id(comp->comp_id, class->level,
> +						     affinity);
> +		if (err)
> +			return err;
> +
> +		if (cpumask_empty(affinity))
> +			pr_warn_once("%s no CPUs associated with cache node",
> +				     dev_name(&msc->pdev->dev));
> +
> +		break;
> +	case MPAM_CLASS_MEMORY:
> +		get_cpumask_from_node_id(comp->comp_id, affinity);
> +		/* affinity may be empty for CPU-less memory nodes */
> +		break;
> +	case MPAM_CLASS_UNKNOWN:
> +		return 0;
> +	}
> +
> +	cpumask_and(affinity, affinity, &msc->accessibility);
> +
> +	return 0;
> +}
> +
> +static int mpam_ris_create_locked(struct mpam_msc *msc, u8 ris_idx,
> +				  enum mpam_class_types type, u8 class_id,
> +				  int component_id)
> +{
> +	int err;
> +	struct mpam_vmsc *vmsc;
> +	struct mpam_msc_ris *ris;
> +	struct mpam_class *class;
> +	struct mpam_component *comp;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	if (ris_idx > MPAM_MSC_MAX_NUM_RIS)
> +		return -EINVAL;
> +
> +	if (test_and_set_bit(ris_idx, &msc->ris_idxs))
> +		return -EBUSY;
> +

Should setting msc->ris_idxs bit be moved to the end of this function 
after all error handling paths? The reason is this bit is better to be 0 
(or recovered) if any error happens. It's hard to recover it to 0 for 
each error handling. The easiest way is to set it at the end of the 
function.

> +	ris = devm_kzalloc(&msc->pdev->dev, sizeof(*ris), GFP_KERNEL);
> +	if (!ris)
> +		return -ENOMEM;
> +	init_garbage(ris);
> +
> +	class = mpam_class_get(class_id, type);
> +	if (IS_ERR(class))
> +		return PTR_ERR(class);
> +
> +	comp = mpam_component_get(class, component_id);
> +	if (IS_ERR(comp)) {
> +		if (list_empty(&class->components))
> +			mpam_class_destroy(class);
> +		return PTR_ERR(comp);
> +	}
> +
> +	vmsc = mpam_vmsc_get(comp, msc);
> +	if (IS_ERR(vmsc)) {
> +		if (list_empty(&comp->vmsc))
> +			mpam_comp_destroy(comp);
> +		return PTR_ERR(vmsc);
> +	}
> +
> +	err = mpam_ris_get_affinity(msc, &ris->affinity, type, class, comp);
> +	if (err) {
> +		if (list_empty(&vmsc->ris))
> +			mpam_vmsc_destroy(vmsc);
> +		return err;
> +	}
> +
> +	ris->ris_idx = ris_idx;
> +	INIT_LIST_HEAD_RCU(&ris->vmsc_list);

vmsc_list will be used but not initialized. Missing 
INIT_LIST_HEAD_RCU(&ris->msc_list) here?

> +	ris->vmsc = vmsc;
> +
> +	cpumask_or(&comp->affinity, &comp->affinity, &ris->affinity);
> +	cpumask_or(&class->affinity, &class->affinity, &ris->affinity);
> +	list_add_rcu(&ris->vmsc_list, &vmsc->ris);
> +
Setting the msc->ris_idxs here is better to avoid to clear it in each 
error handling path.
> +	return 0;
> +}
> +
> +int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
> +		    enum mpam_class_types type, u8 class_id, int component_id)
> +{
> +	int err;
> +
> +	mutex_lock(&mpam_list_lock);
> +	err = mpam_ris_create_locked(msc, ris_idx, type, class_id,
> +				     component_id);
> +	mutex_unlock(&mpam_list_lock);
> +	if (err)
> +		mpam_free_garbage();
> +
> +	return err;
> +}
> +
>   /*
>    * An MSC can control traffic from a set of CPUs, but may only be accessible
>    * from a (hopefully wider) set of CPUs. The common reason for this is power
> @@ -74,10 +469,10 @@ static void mpam_msc_drv_remove(struct platform_device *pdev)
>   		return;
>   
>   	mutex_lock(&mpam_list_lock);
> -	platform_set_drvdata(pdev, NULL);
> -	list_del_rcu(&msc->all_msc_list);
> -	synchronize_srcu(&mpam_srcu);
> +	mpam_msc_destroy(msc);
>   	mutex_unlock(&mpam_list_lock);
> +
> +	mpam_free_garbage();

Should mpam_free_garbage() be protected by mpam_list_lock? It may race 
with adding garbage. I can see other adding and freeing garbage are 
protected by mpam_list_lock but not this one.

>   }
>   
>   static int mpam_msc_drv_probe(struct platform_device *pdev)
> @@ -95,6 +490,7 @@ static int mpam_msc_drv_probe(struct platform_device *pdev)
>   			err = -ENOMEM;
>   			break;
>   		}
> +		init_garbage(msc);
>   
>   		mutex_init(&msc->probe_lock);
>   		mutex_init(&msc->part_sel_lock);
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 7c63d590fc98..02e9576ece6b 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -7,10 +7,29 @@
>   #include <linux/arm_mpam.h>
>   #include <linux/cpumask.h>
>   #include <linux/io.h>
> +#include <linux/llist.h>
>   #include <linux/mailbox_client.h>
>   #include <linux/mutex.h>
>   #include <linux/resctrl.h>
>   #include <linux/sizes.h>
> +#include <linux/srcu.h>
> +
> +#define MPAM_MSC_MAX_NUM_RIS	16
> +
> +/*
> + * Structures protected by SRCU may not be freed for a surprising amount of
> + * time (especially if perf is running). To ensure the MPAM error interrupt can
> + * tear down all the structures, build a list of objects that can be gargbage
> + * collected once synchronize_srcu() has returned.
> + * If pdev is non-NULL, use devm_kfree().
> + */
> +struct mpam_garbage {
> +	/* member of mpam_garbage */
> +	struct llist_node	llist;
> +
> +	void			*to_free;
> +	struct platform_device	*pdev;
> +};
>   
>   struct mpam_msc {
>   	/* member of mpam_all_msc */
> @@ -57,8 +76,79 @@ struct mpam_msc {
>   
>   	void __iomem		*mapped_hwpage;
>   	size_t			mapped_hwpage_sz;
> +
> +	struct mpam_garbage	garbage;
>   };
>   
> +struct mpam_class {
> +	/* mpam_components in this class */
> +	struct list_head	components;
> +
> +	cpumask_t		affinity;
> +
> +	u8			level;
> +	enum mpam_class_types	type;
> +
> +	/* member of mpam_classes */
> +	struct list_head	classes_list;
> +
> +	struct mpam_garbage	garbage;
> +};
> +
> +struct mpam_component {
> +	u32			comp_id;
> +
> +	/* mpam_vmsc in this component */
> +	struct list_head	vmsc;
> +
> +	cpumask_t		affinity;
> +
> +	/* member of mpam_class:components */
> +	struct list_head	class_list;
> +
> +	/* parent: */
> +	struct mpam_class	*class;
> +
> +	struct mpam_garbage	garbage;
> +};
> +
> +struct mpam_vmsc {
> +	/* member of mpam_component:vmsc_list */
> +	struct list_head	comp_list;
> +
> +	/* mpam_msc_ris in this dvmsc */
> +	struct list_head	ris;
> +
> +	/* All RIS in this vMSC are members of this MSC */
> +	struct mpam_msc		*msc;
> +
> +	/* parent: */
> +	struct mpam_component	*comp;
> +
> +	struct mpam_garbage	garbage;
> +};
> +
> +struct mpam_msc_ris {
> +	u8			ris_idx;
> +
> +	cpumask_t		affinity;
> +
> +	/* member of mpam_vmsc:ris */
> +	struct list_head	vmsc_list;
> +
> +	/* member of mpam_msc:ris */
> +	struct list_head	msc_list;
> +
> +	/* parent: */
> +	struct mpam_vmsc	*vmsc;
> +
> +	struct mpam_garbage	garbage;
> +};
> +
> +/* List of all classes - protected by srcu*/
> +extern struct srcu_struct mpam_srcu;
> +extern struct list_head mpam_classes;
> +
>   int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
>   				   cpumask_t *affinity);
>   
> diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
> index 3d6c39c667c3..3206f5ddc147 100644
> --- a/include/linux/arm_mpam.h
> +++ b/include/linux/arm_mpam.h
> @@ -38,11 +38,7 @@ static inline int acpi_mpam_parse_resources(struct mpam_msc *msc,
>   static inline int acpi_mpam_count_msc(void) { return -EINVAL; }
>   #endif
>   
> -static inline int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
> -				  enum mpam_class_types type, u8 class_id,
> -				  int component_id)
> -{
> -	return -EINVAL;
> -}
> +int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
> +		    enum mpam_class_types type, u8 class_id, int component_id);
>   
>   #endif /* __LINUX_ARM_MPAM_H */

Thanks.

-Fenghua

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