[PATCH] elevator: define ioc counting mechanism (4a893e83) · Commits · 戴 / test

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:

Jens Axboe <axboe@suse.de>

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

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