[PATCH] [RFC] Add support for uevents on block device idle changes

Matthew Garrett
2009-11-17T14:38:45Z

Userspace may wish to know whether a given disk is active or idle, for
example to modify power management policy based on access patterns. This
patch adds a deferrable timer to the block layer which will fire if the
disk is idle for a user-definable period of time, generating a uevent. A
uevent will also be generated if an access is received while the disk is
classified as idle.

This patch seems to work as designed, but introduces a noticable amount of
userspace overhead in udevd. I'm guessing that this is because change events
on block devices are normally associated with disk removal/insertion, so
a large quantity of complex rules end up getting run in order to deal with
RAID setup or whatever. Is there a better way to deliver these events?
---
Documentation/ABI/testing/sysfs-block | 9 +++++
block/blk-core.c | 9 +++++
block/genhd.c | 55 +++++++++++++++++++++++++++++++++
fs/partitions/check.c | 3 ++
include/linux/genhd.h | 6 +++
5 files changed, 82 insertions(+), 0 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
index 5f3beda..5519720 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -128,3 +128,12 @@ Description:
preferred request size for workloads where sustained
throughput is desired. If no optimal I/O size is
reported this file contains 0.
+
+What: /sys/block/<disk>/idle_hysteresis
+Date: November 2009
+Contact: Matthew Garrett <mjg@redhat.com>
+Description:
+ Contains the number of milliseconds to wait after an access
+ before declaring that a disk is idle. Any accesses during
+ this time will reset the timer. "0" (the default) indicates
+ that no events will be generated.
\ No newline at end of file
diff --git a/block/blk-core.c b/block/blk-core.c
index 71da511..f278817 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1452,6 +1452,15 @@ static inline void __generic_make_request(struct bio *bio)
if (should_fail_request(bio))
goto end_io;

+ if (bio->bi_bdev->bd_disk->hysteresis_time &&
+ bio_has_data(bio) &&
+ !mod_timer(&bio->bi_bdev->bd_disk->hysteresis_timer,
+ jiffies+msecs_to_jiffies
+ (bio->bi_bdev->bd_disk->hysteresis_time))) {
+ bio->bi_bdev->bd_disk->idle = 0;
+ schedule_work(&bio->bi_bdev->bd_disk->idle_notify);
+ }
+
/*
* If this device has partitions, remap block n
* of partition p to block n+start(p) of the disk.
diff --git a/block/genhd.c b/block/genhd.c
index 517e433..f59fbe0 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -504,6 +504,26 @@ static int exact_lock(dev_t devt, void *data)
return 0;
}

+static void disk_idle(unsigned long data)
+{
+ struct gendisk *gd = (struct gendisk *)data;
+
+ gd->idle = 1;
+ schedule_work(&gd->idle_notify);
+}
+
+static void disk_idle_notify_thread(struct work_struct *work)
+{
+ struct gendisk *gd = container_of(work, struct gendisk, idle_notify);
+ char event[] = "IDLE=0";
+ char *envp[] = { event, NULL };
+
+ if (gd->idle)
+ event[5] = '1';
+
+ kobject_uevent_env(&disk_to_dev(gd)->kobj, KOBJ_CHANGE, envp);
+}
+
/**
* add_disk - add partitioning information to kernel list
* @disk: per-device partitioning information
@@ -543,6 +563,10 @@ void add_disk(struct gendisk *disk)

blk_register_region(disk_devt(disk), disk->minors, NULL,
exact_match, exact_lock, disk);
+
+ init_timer(&disk->hysteresis_timer);
+ setup_timer(&disk->hysteresis_timer, disk_idle, (unsigned long)disk);
+
register_disk(disk);
blk_register_queue(disk);

@@ -861,6 +885,32 @@ static ssize_t disk_alignment_offset_show(struct device *dev,
return sprintf(buf, "%d\n", queue_alignment_offset(disk->queue));
}

+static ssize_t disk_idle_hysteresis_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct gendisk *disk = dev_to_disk(dev);
+
+ return sprintf(buf, "%d\n", disk->hysteresis_time);
+}
+
+static ssize_t disk_idle_hysteresis_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct gendisk *disk = dev_to_disk(dev);
+ unsigned long timeout;
+ int res;
+
+ res = strict_strtoul(buf, 10, &timeout);
+ if (res)
+ return -EINVAL;
+
+ disk->hysteresis_time = timeout;
+
+ return count;
+}
+
static DEVICE_ATTR(range, S_IRUGO, disk_range_show, NULL);
static DEVICE_ATTR(ext_range, S_IRUGO, disk_ext_range_show, NULL);
static DEVICE_ATTR(removable, S_IRUGO, disk_removable_show, NULL);
@@ -870,6 +920,8 @@ static DEVICE_ATTR(alignment_offset, S_IRUGO, disk_alignment_offset_show, NULL);
static DEVICE_ATTR(capability, S_IRUGO, disk_capability_show, NULL);
static DEVICE_ATTR(stat, S_IRUGO, part_stat_show, NULL);
static DEVICE_ATTR(inflight, S_IRUGO, part_inflight_show, NULL);
+static DEVICE_ATTR(idle_hysteresis, 0644, disk_idle_hysteresis_show,
+ disk_idle_hysteresis_store);
#ifdef CONFIG_FAIL_MAKE_REQUEST
static struct device_attribute dev_attr_fail =
__ATTR(make-it-fail, S_IRUGO|S_IWUSR, part_fail_show, part_fail_store);
@@ -890,6 +942,7 @@ static struct attribute *disk_attrs[] = {
&dev_attr_capability.attr,
&dev_attr_stat.attr,
&dev_attr_inflight.attr,
+ &dev_attr_idle_hysteresis.attr,
#ifdef CONFIG_FAIL_MAKE_REQUEST
&dev_attr_fail.attr,
#endif
@@ -1183,6 +1236,8 @@ struct gendisk *alloc_disk_node(int minors, int node_id)
device_initialize(disk_to_dev(disk));
INIT_WORK(&disk->async_notify,
media_change_notify_thread);
+ INIT_WORK(&disk->idle_notify,
+ disk_idle_notify_thread);
}
return disk;
}
diff --git a/fs/partitions/check.c b/fs/partitions/check.c
index 7b685e1..d55dd29 100644
--- a/fs/partitions/check.c
+++ b/fs/partitions/check.c
@@ -652,6 +652,9 @@ void del_gendisk(struct gendisk *disk)
struct disk_part_iter piter;
struct hd_struct *part;

+ cancel_work_sync(&disk->idle_notify);
+ del_timer_sync(&disk->hysteresis_timer);
+
/* invalidate stuff */
disk_part_iter_init(&piter, disk,
DISK_PITER_INCL_EMPTY | DISK_PITER_REVERSE);
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 297df45..7e969a5 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -12,6 +12,7 @@
#include <linux/types.h>
#include <linux/kdev_t.h>
#include <linux/rcupdate.h>
+#include <linux/timer.h>

#ifdef CONFIG_BLOCK

@@ -163,10 +164,15 @@ struct gendisk {

atomic_t sync_io; /* RAID */
struct work_struct async_notify;
+ struct work_struct idle_notify;
#ifdef CONFIG_BLK_DEV_INTEGRITY
struct blk_integrity *integrity;
#endif
int node_id;
+
+ bool idle;
+ int hysteresis_time;
+ struct timer_list hysteresis_timer;
};

static inline struct gendisk *part_to_disk(struct hd_struct *part)
--
1.6.5.2