On Tue, 8 May 2007 20:48:59 +0100
Alasdair G Kergon <agk@xxxxxxxxxx> wrote:
> From: Heinz Mauelshagen <mauelshagen@xxxxxxxxxx>
>
> New device-mapper target that can delay I/O (for testing).
> Reads can be separated from writes, redirected to different underlying
> devices and delayed by differing amounts of time.
>
> ..
>
> +/*
> + * Copyright (C) 2005-2007 Red Hat GmbH
> + *
> + * A target that delays reads and/or writes and can send
> + * them to different devices.
> + *
> + * This file is released under the GPL.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/blkdev.h>
> +#include <linux/bio.h>
> +#include <linux/slab.h>
> +
> +#include "dm.h"
> +#include "dm-bio-list.h"
> +
> +#define DM_MSG_PREFIX "delay"
> +
> +struct delay_c {
> + struct timer_list delay_timer;
> + struct semaphore timer_lock;
Can we get this converted to a mutex asap, please?
It's only used in a single place and perhaps we don't need this lock at
all?
> + struct work_struct flush_expired_bios;
> + struct list_head delayed_bios;
> + atomic_t may_delay;
> + mempool_t *delayed_pool;
> +
> + struct dm_dev *dev_read;
> + sector_t start_read;
> + unsigned read_delay;
> + unsigned reads;
> +
> + struct dm_dev *dev_write;
> + sector_t start_write;
> + unsigned write_delay;
> + unsigned writes;
> +};
> +
> +struct delay_info {
> + struct delay_c *context;
> + struct list_head list;
> + struct bio *bio;
> + unsigned long expires;
> +};
> +
> +static DEFINE_MUTEX(delayed_bios_lock);
> +
> +static struct workqueue_struct *kdelayd_wq;
> +static struct kmem_cache *delayed_cache;
> +
> +static void handle_delayed_timer(unsigned long data)
> +{
> + struct delay_c *dc = (struct delay_c *)data;
> +
> + queue_work(kdelayd_wq, &dc->flush_expired_bios);
> +}
> +
> +static void queue_timeout(struct delay_c *dc, unsigned long expires)
> +{
> + down(&dc->timer_lock);
> +
> + if (!timer_pending(&dc->delay_timer) || expires < dc->delay_timer.expires)
> + mod_timer(&dc->delay_timer, expires);
> +
> + up(&dc->timer_lock);
> +}
>
> ...
>
> +
> + init_timer(&dc->delay_timer);
> + dc->delay_timer.function = handle_delayed_timer;
> + dc->delay_timer.data = (unsigned long)dc;
setup_timer() could be used here.
> + INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
> + INIT_LIST_HEAD(&dc->delayed_bios);
> + init_MUTEX(&dc->timer_lock);
> + atomic_set(&dc->may_delay, 1);
> +
> + ti->private = dc;
> + return 0;
> +
> +bad:
> + kfree(dc);
> + return -EINVAL;
> +}
> +
>
> ...
>
> +
> +static int __init dm_delay_init(void)
> +{
> + int r = -ENOMEM;
> +
> + kdelayd_wq = create_workqueue("kdelayd");
> + if (!kdelayd_wq) {
> + DMERR("Couldn't start kdelayd");
> + goto bad_queue;
> + }
Do we really really need one instance of kdelayd on each CPU?
I suspect a single-threaded workqueue would suffice here. We have a big
global lock in this driver anyway....
Probably create_workqueue() should have defaulted to single-threaded on day
one. Oh well.
> + delayed_cache = kmem_cache_create("dm-delay",
> + sizeof(struct delay_info),
> + __alignof__(struct delay_info),
> + 0, NULL, NULL);
We have an ugly^Wnice new KMEM_CACHE macro for this now.
What's that __alignof__ doing in there?
> + if (!delayed_cache) {
> + DMERR("Couldn't create delayed bio cache.");
> + goto bad_memcache;
> + }
> +
> + r = dm_register_target(&delay_target);
> + if (r < 0) {
> + DMERR("register failed %d", r);
> + goto bad_register;
> + }
> +
> + return 0;
> +
> +bad_register:
> + kmem_cache_destroy(delayed_cache);
> +bad_memcache:
> + destroy_workqueue(kdelayd_wq);
> +bad_queue:
> + return r;
> +}
> +
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