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Commit 8d354f13 authored by Jens Axboe's avatar Jens Axboe
Browse files

blk-mq: improve layout of blk_mq_hw_ctx 



Various cache line optimizations:

- Move delay_work towards the end. It's huge, and we don't use it
  a lot (only SCSI).

- Move the atomic state into the same cacheline as the the dispatch
  list and lock.

- Rearrange a few members to pack it better.

- Shrink the max-order for dispatch accounting from 10 to 7. This
  means that ->dispatched[] and ->run now take up their own
  cacheline.

This shrinks struct blk_mq_hw_ctx down to 8 cachelines.

Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 27489a3c

include/linux/blk-mq.h

+5 −4
Original line number Diff line number Diff line
@@ -22,11 +22,10 @@ struct blk_mq_hw_ctx { 
	struct {

		spinlock_t		lock;

		struct list_head	dispatch;

		unsigned long		state;		/* BLK_MQ_S_* flags */

	} ____cacheline_aligned_in_smp;



	unsigned long		state;		/* BLK_MQ_S_* flags */

	struct work_struct	run_work;

	struct delayed_work	delay_work;

	cpumask_var_t		cpumask;

	int			next_cpu;

	int			next_cpu_batch;
@@ -40,8 +39,8 @@ struct blk_mq_hw_ctx { 


	struct blk_mq_ctxmap	ctx_map;



	unsigned int		nr_ctx;

	struct blk_mq_ctx	**ctxs;

	unsigned int		nr_ctx;



	atomic_t		wait_index;
@@ -49,7 +48,7 @@ struct blk_mq_hw_ctx { 


	unsigned long		queued;

	unsigned long		run;

#define BLK_MQ_MAX_DISPATCH_ORDER	10

#define BLK_MQ_MAX_DISPATCH_ORDER	7

	unsigned long		dispatched[BLK_MQ_MAX_DISPATCH_ORDER];



	unsigned int		numa_node;
@@ -57,6 +56,8 @@ struct blk_mq_hw_ctx { 


	atomic_t		nr_active;



	struct delayed_work	delay_work;



	struct blk_mq_cpu_notifier	cpu_notifier;

	struct kobject		kobj;