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Commit 4a893e83 authored by Jens Axboe's avatar Jens Axboe Committed by Jens Axboe
Browse files

[PATCH] elevator: define ioc counting mechanism 



None of the in-kernel primitives for handling "atomic" counting seem
to be a good fit. We need something that is essentially free for
incrementing/decrementing, while the read side may be more expensive
as we only ever need to do that when a device is removed from the
kernel.

Use a per-cpu variable for maintaining a per-cpu ioc count and define
a reading mechanism that just sums up the values.

Signed-off-by: default avatarJens Axboe <axboe@suse.de>
parent fc46379d

include/linux/elevator.h

+25 −0
Original line number Diff line number Diff line 
#ifndef _LINUX_ELEVATOR_H

#define _LINUX_ELEVATOR_H



#include <linux/percpu.h>



typedef int (elevator_merge_fn) (request_queue_t *, struct request **,

				 struct bio *);
@@ -178,4 +180,27 @@ enum { 
	INIT_LIST_HEAD(&(rq)->donelist);	\

	} while (0)



/*

 * io context count accounting

 */

#define elv_ioc_count_mod(name, __val)				\

	do {							\

		preempt_disable();				\

		__get_cpu_var(name) += (__val);			\

		preempt_enable();				\

	} while (0)



#define elv_ioc_count_inc(name)	elv_ioc_count_mod(name, 1)

#define elv_ioc_count_dec(name)	elv_ioc_count_mod(name, -1)



#define elv_ioc_count_read(name)				\

({								\

	unsigned long __val = 0;				\

	int __cpu;						\

	smp_wmb();						\

	for_each_possible_cpu(__cpu)				\

		__val += per_cpu(name, __cpu);			\

	__val;							\

})



#endif