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Revision 153d7f3fcae7ed4e19328549aa9467acdfbced10 authored by Arjan van de Ven on 26 July 2006, 13:40:07 UTC, committed by Linus Torvalds on 26 July 2006, 14:21:40 UTC 
[PATCH] Reorganize the cpufreq cpu hotplug locking to not be totally bizare
 
The patch below moves the cpu hotplugging higher up in the cpufreq
layering; this is needed to avoid recursive taking of the cpu hotplug
lock and to otherwise detangle the mess.

The new rules are:
1. you must do lock_cpu_hotplug() around the following functions:
   __cpufreq_driver_target
   __cpufreq_governor (for CPUFREQ_GOV_LIMITS operation only)
   __cpufreq_set_policy
2. governer methods (.governer) must NOT take the lock_cpu_hotplug()
   lock in any way; they are called with the lock taken already
3. if your governer spawns a thread that does things, like calling
   __cpufreq_driver_target, your thread must honor rule #1.
4. the policy lock and other cpufreq internal locks nest within
   the lock_cpu_hotplug() lock.

I'm not entirely happy about how the __cpufreq_governor rule ended up
(conditional locking rule depending on the argument) but basically all
callers pass this as a constant so it's not too horrible.

The patch also removes the cpufreq_governor() function since during the
locking audit it turned out to be entirely unused (so no need to fix it)

The patch works on my testbox, but it could use more testing
(otoh... it can't be much worse than the current code)

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 parent 44eb123
Raw File
noop-iosched.c 
/*
 * elevator noop
 */
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/init.h>

struct noop_data {
	struct list_head queue;
};

static void noop_merged_requests(request_queue_t *q, struct request *rq,
				 struct request *next)
{
	list_del_init(&next->queuelist);
}

static int noop_dispatch(request_queue_t *q, int force)
{
	struct noop_data *nd = q->elevator->elevator_data;

	if (!list_empty(&nd->queue)) {
		struct request *rq;
		rq = list_entry(nd->queue.next, struct request, queuelist);
		list_del_init(&rq->queuelist);
		elv_dispatch_sort(q, rq);
		return 1;
	}
	return 0;
}

static void noop_add_request(request_queue_t *q, struct request *rq)
{
	struct noop_data *nd = q->elevator->elevator_data;

	list_add_tail(&rq->queuelist, &nd->queue);
}

static int noop_queue_empty(request_queue_t *q)
{
	struct noop_data *nd = q->elevator->elevator_data;

	return list_empty(&nd->queue);
}

static struct request *
noop_former_request(request_queue_t *q, struct request *rq)
{
	struct noop_data *nd = q->elevator->elevator_data;

	if (rq->queuelist.prev == &nd->queue)
		return NULL;
	return list_entry(rq->queuelist.prev, struct request, queuelist);
}

static struct request *
noop_latter_request(request_queue_t *q, struct request *rq)
{
	struct noop_data *nd = q->elevator->elevator_data;

	if (rq->queuelist.next == &nd->queue)
		return NULL;
	return list_entry(rq->queuelist.next, struct request, queuelist);
}

static void *noop_init_queue(request_queue_t *q, elevator_t *e)
{
	struct noop_data *nd;

	nd = kmalloc(sizeof(*nd), GFP_KERNEL);
	if (!nd)
		return NULL;
	INIT_LIST_HEAD(&nd->queue);
	return nd;
}

static void noop_exit_queue(elevator_t *e)
{
	struct noop_data *nd = e->elevator_data;

	BUG_ON(!list_empty(&nd->queue));
	kfree(nd);
}

static struct elevator_type elevator_noop = {
	.ops = {
		.elevator_merge_req_fn		= noop_merged_requests,
		.elevator_dispatch_fn		= noop_dispatch,
		.elevator_add_req_fn		= noop_add_request,
		.elevator_queue_empty_fn	= noop_queue_empty,
		.elevator_former_req_fn		= noop_former_request,
		.elevator_latter_req_fn		= noop_latter_request,
		.elevator_init_fn		= noop_init_queue,
		.elevator_exit_fn		= noop_exit_queue,
	},
	.elevator_name = "noop",
	.elevator_owner = THIS_MODULE,
};

static int __init noop_init(void)
{
	return elv_register(&elevator_noop);
}

static void __exit noop_exit(void)
{
	elv_unregister(&elevator_noop);
}

module_init(noop_init);
module_exit(noop_exit);


MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("No-op IO scheduler");
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