Re: [PATCHv5 08/10] node: Add memory caching attributes

Jonathan Cameron
2019-02-06T12:24:35Z

On Thu, 24 Jan 2019 16:07:22 -0700
Keith Busch <keith.busch@intel.com> wrote:

> System memory may have side caches to help improve access speed to
> frequently requested address ranges. While the system provided cache is
> transparent to the software accessing these memory ranges, applications
> can optimize their own access based on cache attributes.
>
> Provide a new API for the kernel to register these memory side caches
> under the memory node that provides it.
>
> The new sysfs representation is modeled from the existing cpu cacheinfo
> attributes, as seen from /sys/devices/system/cpu/<cpu>/side_cache/.
<cpu>/cache/?

> Unlike CPU cacheinfo though, the node cache level is reported from
> the view of the memory. A higher number is nearer to the CPU, while
> lower levels are closer to the backing memory. Also unlike CPU cache,
> it is assumed the system will handle flushing any dirty cached memory
> to the last level on a power failure if the range is persistent memory.
That's a design choice. A sensible one perhaps, but not a requirement of
this infrastructure. Not that it really matters as who reads patch
descriptions after they are applied? :)

>
> The attributes we export are the cache size, the line size, associativity,
> and write back policy.
>
> Add the attributes for the system memory side caches to sysfs stable
> documentation.
>
> Signed-off-by: Keith Busch <keith.busch@intel.com>
A few minor points inline.

> ---
> Documentation/ABI/stable/sysfs-devices-node | 34 +++++++
> drivers/base/node.c | 153 ++++++++++++++++++++++++++++
> include/linux/node.h | 34 +++++++
> 3 files changed, 221 insertions(+)
>
> diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
> index 41cb9345e1e0..26327279b6b6 100644
> --- a/Documentation/ABI/stable/sysfs-devices-node
> +++ b/Documentation/ABI/stable/sysfs-devices-node
> @@ -142,3 +142,37 @@ Contact: Keith Busch <keith.busch@intel.com>
> Description:
> This node's write latency in nanoseconds when access
> from nodes found in this class's linked initiators.
> +
> +What: /sys/devices/system/node/nodeX/side_cache/indexY/associativity
> +Date: December 2018
> +Contact: Keith Busch <keith.busch@intel.com>
> +Description:
> + The caches associativity: 0 for direct mapped, non-zero if
> + indexed.
> +
> +What: /sys/devices/system/node/nodeX/side_cache/indexY/level
> +Date: December 2018
> +Contact: Keith Busch <keith.busch@intel.com>
> +Description:
> + This cache's level in the memory hierarchy. Matches 'Y' in the
> + directory name.

Mentioned in the docs, but I'm not sure why we need this given it matches the
directory name in which it is found... For the cpu caches they aren't the
same (data vs instruction) for example.

> +
> +What: /sys/devices/system/node/nodeX/side_cache/indexY/line_size
> +Date: December 2018
> +Contact: Keith Busch <keith.busch@intel.com>
> +Description:
> + The number of bytes accessed from the next cache level on a
> + cache miss.
> +
> +What: /sys/devices/system/node/nodeX/side_cache/indexY/size
> +Date: December 2018
> +Contact: Keith Busch <keith.busch@intel.com>
> +Description:
> + The size of this memory side cache in bytes.
> +
> +What: /sys/devices/system/node/nodeX/side_cache/indexY/write_policy
> +Date: December 2018
> +Contact: Keith Busch <keith.busch@intel.com>
> +Description:
> + The cache write policy: 0 for write-back, 1 for write-through,
> + other or unknown.
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 2de546a040a5..9b4cb29863ff 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -205,6 +205,157 @@ void node_set_perf_attrs(unsigned int nid, struct node_hmem_attrs *hmem_attrs,
> }
> }
> }
> +
> +/**
> + * struct node_cache_info - Internal tracking for memory node caches
> + * @dev: Device represeting the cache level
> + * @node: List element for tracking in the node
> + * @cache_attrs:Attributes for this cache level
> + */
> +struct node_cache_info {
> + struct device dev;
> + struct list_head node;
> + struct node_cache_attrs cache_attrs;
> +};
> +#define to_cache_info(device) container_of(device, struct node_cache_info, dev)
> +
> +#define CACHE_ATTR(name, fmt) \
> +static ssize_t name##_show(struct device *dev, \
> + struct device_attribute *attr, \
> + char *buf) \
> +{ \
> + return sprintf(buf, fmt "\n", to_cache_info(dev)->cache_attrs.name);\
> +} \
> +DEVICE_ATTR_RO(name);
> +
> +CACHE_ATTR(size, "%llu")
> +CACHE_ATTR(level, "%u")
> +CACHE_ATTR(line_size, "%u")
> +CACHE_ATTR(associativity, "%u")
> +CACHE_ATTR(write_policy, "%u")
> +
> +static struct attribute *cache_attrs[] = {
> + &dev_attr_level.attr,
> + &dev_attr_associativity.attr,
> + &dev_attr_size.attr,
> + &dev_attr_line_size.attr,
> + &dev_attr_write_policy.attr,
> + NULL,
> +};
> +ATTRIBUTE_GROUPS(cache);
> +
> +static void node_cache_release(struct device *dev)
> +{
> + kfree(dev);
> +}
> +
> +static void node_cacheinfo_release(struct device *dev)
> +{
> + struct node_cache_info *info = to_cache_info(dev);
> + kfree(info);
> +}
> +
> +static void node_init_cache_dev(struct node *node)
> +{
> + struct device *dev;
> +
> + dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> + if (!dev)
> + return;
> +
> + dev->parent = &node->dev;
> + dev->release = node_cache_release;
> + if (dev_set_name(dev, "side_cache"))
> + goto free_dev;
> +
> + if (device_register(dev))
> + goto free_name;
> +
> + pm_runtime_no_callbacks(dev);
> + node->cache_dev = dev;
> + return;
> +free_name:
> + kfree_const(dev->kobj.name);
> +free_dev:
> + kfree(dev);
> +}
> +
> +/**
> + * node_add_cache - add cache attribute to a memory node
This is almost but not quite in kernel-doc.
node_add_cache() - add

IIRC.

> + * @nid: Node identifier that has new cache attributes
> + * @cache_attrs: Attributes for the cache being added
> + */
> +void node_add_cache(unsigned int nid, struct node_cache_attrs *cache_attrs)
> +{
> + struct node_cache_info *info;
> + struct device *dev;
> + struct node *node;
> +
> + if (!node_online(nid) || !node_devices[nid])
> + return;
> +
> + node = node_devices[nid];
> + list_for_each_entry(info, &node->cache_attrs, node) {
> + if (info->cache_attrs.level == cache_attrs->level) {
> + dev_warn(&node->dev,
> + "attempt to add duplicate cache level:%d\n",
> + cache_attrs->level);
> + return;
> + }
> + }
> +
> + if (!node->cache_dev)
> + node_init_cache_dev(node);
> + if (!node->cache_dev)
> + return;
> +
> + info = kzalloc(sizeof(*info), GFP_KERNEL);
> + if (!info)
> + return;
> +
> + dev = &info->dev;
> + dev->parent = node->cache_dev;
> + dev->release = node_cacheinfo_release;
> + dev->groups = cache_groups;
> + if (dev_set_name(dev, "index%d", cache_attrs->level))
> + goto free_cache;
> +
> + info->cache_attrs = *cache_attrs;
> + if (device_register(dev)) {
> + dev_warn(&node->dev, "failed to add cache level:%d\n",
> + cache_attrs->level);
> + goto free_name;
> + }
> + pm_runtime_no_callbacks(dev);
> + list_add_tail(&info->node, &node->cache_attrs);
> + return;
> +free_name:
> + kfree_const(dev->kobj.name);
> +free_cache:
> + kfree(info);
> +}
> +
> +static void node_remove_caches(struct node *node)
> +{
> + struct node_cache_info *info, *next;
> +
> + if (!node->cache_dev)
> + return;
> +
> + list_for_each_entry_safe(info, next, &node->cache_attrs, node) {
> + list_del(&info->node);
> + device_unregister(&info->dev);
> + }
> + device_unregister(node->cache_dev);
> +}
> +
> +static void node_init_caches(unsigned int nid)
> +{
> + INIT_LIST_HEAD(&node_devices[nid]->cache_attrs);
> +}
> +#else
> +static void node_init_caches(unsigned int nid) { }
> +static void node_remove_caches(struct node *node) { }
> #endif
>
> #define K(x) ((x) << (PAGE_SHIFT - 10))
> @@ -489,6 +640,7 @@ void unregister_node(struct node *node)
> {
> hugetlb_unregister_node(node); /* no-op, if memoryless node */
> node_remove_accesses(node);
> + node_remove_caches(node);
> device_unregister(&node->dev);
> }
>
> @@ -781,6 +933,7 @@ int __register_one_node(int nid)
> INIT_LIST_HEAD(&node_devices[nid]->access_list);
> /* initialize work queue for memory hot plug */
> init_node_hugetlb_work(nid);
> + node_init_caches(nid);
>
> return error;
> }
> diff --git a/include/linux/node.h b/include/linux/node.h
> index 2db077363d9c..842e4ab2ae6d 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -37,6 +37,36 @@ struct node_hmem_attrs {
> };
> void node_set_perf_attrs(unsigned int nid, struct node_hmem_attrs *hmem_attrs,
> unsigned access);
> +
> +enum cache_associativity {
> + NODE_CACHE_DIRECT_MAP,
> + NODE_CACHE_INDEXED,
> + NODE_CACHE_OTHER,
> +};
> +
> +enum cache_write_policy {
> + NODE_CACHE_WRITE_BACK,
> + NODE_CACHE_WRITE_THROUGH,
> + NODE_CACHE_WRITE_OTHER,
> +};
> +
> +/**
> + * struct node_cache_attrs - system memory caching attributes
> + *
> + * @associativity: The ways memory blocks may be placed in cache
> + * @write_policy: Write back or write through policy
> + * @size: Total size of cache in bytes
> + * @line_size: Number of bytes fetched on a cache miss
> + * @level: Represents the cache hierarchy level
> + */
> +struct node_cache_attrs {
> + enum cache_associativity associativity;
> + enum cache_write_policy write_policy;
> + u64 size;
> + u16 line_size;
> + u8 level;
> +};
> +void node_add_cache(unsigned int nid, struct node_cache_attrs *cache_attrs);
> #endif
>
> struct node {
> @@ -45,6 +75,10 @@ struct node {
> #if defined(CONFIG_MEMORY_HOTPLUG_SPARSE) && defined(CONFIG_HUGETLBFS)
> struct work_struct node_work;
> #endif
> +#ifdef CONFIG_HMEM_REPORTING
> + struct list_head cache_attrs;
> + struct device *cache_dev;
> +#endif
> };
>
> struct memory_block;