device.h: reorganize struct device (159ef31e) · Commits · 戴 / test

struct device is big, around 760 bytes on x86_64. It's not a critical structure, but it is embedded everywhere, so making it smaller is always a good thing. With a recent patch that moved a field from struct device to the private structure, some benchmarks showed a very odd regression, despite this structure having nothing to do with those benchmarks. That caused me to look into the layout of the structure. Using 'pahole', it showed a number of holes and ways that the structure could be reordered in order to align some cachelines better, as well as reduce the size of the overall structure. Move 'struct kobj' to the start of the structure, to keep that access in the first cacheline, and try to organize things a bit more compactly where possible By doing these few moves, the result removes at least 8 bytes from 'struct device' on a 64bit system. Given we know there are systems with at least 30k devices in memory at once, every little byte counts, and this change could be a savings of 240k of kernel memory for them. On "normal" systems the overall memory savings would be much less. Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> Cc: Johan Hovold <johan@kernel.org> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/device.h

+8 −8

Original line number	Diff line number	Diff line
		@@ -976,18 +976,14 @@ struct dev_links_info {
		* a higher-level representation of the device.
		*/
		struct device {
		struct kobject kobj;
		struct device *parent;

		struct device_private *p;

		struct kobject kobj;
		const char init_name; / initial name of the device */
		const struct device_type *type;

		struct mutex mutex; /* mutex to synchronize calls to
		* its driver.
		*/

		struct bus_type bus; / type of bus device is on */
		struct device_driver driver; / which driver has allocated this
		device */
		@@ -995,6 +991,10 @@ struct device {
		core doesn't touch it */
		void driver_data; / Driver data, set and get with
		dev_set_drvdata/dev_get_drvdata */
		struct mutex mutex; /* mutex to synchronize calls to
		* its driver.
		*/

		struct dev_links_info links;
		struct dev_pm_info power;
		struct dev_pm_domain *pm_domain;
		@@ -1009,9 +1009,6 @@ struct device {
		struct list_head msi_list;
		#endif

		#ifdef CONFIG_NUMA
		int numa_node; /* NUMA node this device is close to */
		#endif
		const struct dma_map_ops *dma_ops;
		u64 dma_mask; / dma mask (if dma'able device) */
		u64 coherent_dma_mask;/* Like dma_mask, but for
		@@ -1040,6 +1037,9 @@ struct device {
		struct device_node of_node; / associated device tree node */
		struct fwnode_handle fwnode; / firmware device node */

		#ifdef CONFIG_NUMA
		int numa_node; /* NUMA node this device is close to */
		#endif
		dev_t devt; /* dev_t, creates the sysfs "dev" */
		u32 id; /* device instance */

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