Elias Oltmanns <eo@xxxxxxxxxxxxxx> wrote:
> Pavel Machek <pavel@xxxxxx> wrote:
>> On Fri 2008-03-07 19:26:41, Elias Oltmanns wrote:
>>> This patch provides a generic way to freeze the request queue of a block
>>> device temporarily. This functionality is exposed to user space via sysfs.
>>>
>>> Signed-off-by: Elias Oltmanns <eo@xxxxxxxxxxxxxx>
[...]
>>> +/*
>>> + * When reading the 'protect' attribute, we return seconds remaining
>>> + * before the unfreeze timeout expires.
>>> + */
>>> +static ssize_t queue_protect_show(struct request_queue *q, char *page)
>>> +{
>>> + unsigned int seconds = 0;
>>> +
>>> + if (blk_queue_stopped(q) && timer_pending(&q->unfreeze_timer))
>>> + /*
>>> + * Adding 1 in order to guarantee nonzero value until timer
>>> + * has actually expired.
>>> + */
>>> + seconds = jiffies_to_msecs(q->unfreeze_timer.expires
>>> + - jiffies) / 1000 + 1;
>>
>> Is it okay to read expires without locking?
>
> No, I have been a bit careless with regard to locking in this patch. See
> the revised version below.
Come to think of it, the lock really shouldn't be released between
modding / checking the timer and issuing the respective command. This
makes the whole thing a bit messy because allocating a request the
standard way is done before acquiring the spin_lock. Since we don't know
at that time whether a command is actually going to be enqueued, this
looks rather suboptimal to me. A better idea anyone?
Regards,
Elias
---
block/ll_rw_blk.c | 142 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/blkdev.h | 7 ++
2 files changed, 149 insertions(+), 0 deletions(-)
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 8b91994..112af66 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -39,6 +39,8 @@
static void blk_unplug_work(struct work_struct *work);
static void blk_unplug_timeout(unsigned long data);
+static void blk_unfreeze_work(struct work_struct *work);
+static void blk_unfreeze_timeout(unsigned long data);
static void drive_stat_acct(struct request *rq, int new_io);
static void init_request_from_bio(struct request *req, struct bio *bio);
static int __make_request(struct request_queue *q, struct bio *bio);
@@ -231,6 +233,13 @@ void blk_queue_make_request(struct request_queue * q, make_request_fn * mfn)
q->unplug_timer.function = blk_unplug_timeout;
q->unplug_timer.data = (unsigned long)q;
+ q->max_unfreeze = 30;
+
+ INIT_WORK(&q->unfreeze_work, blk_unfreeze_work);
+
+ q->unfreeze_timer.function = blk_unfreeze_timeout;
+ q->unfreeze_timer.data = (unsigned long)q;
+
/*
* by default assume old behaviour and bounce for any highmem page
*/
@@ -1861,6 +1870,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
}
init_timer(&q->unplug_timer);
+ init_timer(&q->unfreeze_timer);
kobject_set_name(&q->kobj, "%s", "queue");
q->kobj.ktype = &queue_ktype;
@@ -1975,6 +1985,92 @@ int blk_get_queue(struct request_queue *q)
EXPORT_SYMBOL(blk_get_queue);
+static void issue_queue_freeze_cmd(struct request_queue *q,
+ struct request *rq, int thaw)
+{
+ rq->cmd_type = REQ_TYPE_LINUX_BLOCK;
+ rq->cmd_len = 1;
+ rq->cmd_flags |= REQ_NOMERGE | REQ_SOFTBARRIER;
+ if (thaw)
+ rq->cmd[0] = REQ_LB_OP_THAW;
+ else
+ rq->cmd[0] = REQ_LB_OP_FREEZE;
+ rq->rq_disk = NULL;
+ rq->sense = NULL;
+ rq->sense_len = 0;
+ rq->retries = 5;
+ rq->timeout = HZ;
+ __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
+ if (thaw)
+ blk_start_queue(q);
+ else {
+ blk_stop_queue(q);
+ q->request_fn(q);
+ }
+}
+
+static void blk_unfreeze_work(struct work_struct *work)
+{
+ struct request_queue *q = container_of(work, struct request_queue,
+ unfreeze_work);
+ struct request *rq;
+
+ rq = blk_get_request(q, 0, __GFP_WAIT);
+ spin_lock_irq(q->queue_lock);
+ if (!timer_pending(&q->unfreeze_timer))
+ issue_queue_freeze_cmd(q, rq, 1);
+ else
+ __blk_put_request(q, rq);
+ spin_unlock_irq(q->queue_lock);
+}
+
+static void blk_unfreeze_timeout(unsigned long data)
+{
+ struct request_queue *q = (struct request_queue *) data;
+
+ kblockd_schedule_work(&q->unfreeze_work);
+}
+
+/**
+ * blk_freeze_queue - (un)freeze queue and manage the queue unfreeze timer
+ * @q: queue to be (un)frozen
+ * @second: number of seconds to freeze the queue for
+ *
+ * Description: This function (re)sets the unfreeze timer of a request
+ * queue. When a timer is started / stopped (not just modified),
+ * then low level drivers are notified about this event.
+ */
+static int blk_freeze_queue(struct request_queue *q, unsigned int seconds)
+{
+ struct request *rq;
+ int rc;
+
+ rq = blk_get_request(q, 0, __GFP_HIGH | __GFP_WAIT);
+ spin_lock_irq(q->queue_lock);
+ if (seconds > 0) {
+ if (seconds > q->max_unfreeze)
+ seconds = q->max_unfreeze;
+ /* set / reset the thaw timer */
+ rc = !mod_timer(&q->unfreeze_timer,
+ msecs_to_jiffies(seconds * 1000) + jiffies);
+ if (rc && blk_queue_stopped(q)) {
+ /* Someone else has stopped the queue already.
+ * Best leave it alone.
+ */
+ del_timer(&q->unfreeze_timer);
+ rc = 0;
+ }
+ } else
+ rc = del_timer(&q->unfreeze_timer);
+ if (rc)
+ issue_queue_freeze_cmd(q, rq, !seconds);
+ else
+ __blk_put_request(q, rq);
+ spin_unlock_irq(q->queue_lock);
+
+ return rc;
+}
+
static inline void blk_free_request(struct request_queue *q, struct request *rq)
{
if (rq->cmd_flags & REQ_ELVPRIV)
@@ -4080,6 +4176,45 @@ static ssize_t queue_max_hw_sectors_show(struct request_queue *q, char *page)
return queue_var_show(max_hw_sectors_kb, (page));
}
+/*
+ * When reading the 'protect' attribute, we return seconds remaining
+ * before the unfreeze timeout expires.
+ */
+static ssize_t queue_protect_show(struct request_queue *q, char *page)
+{
+ unsigned int seconds = 0;
+
+ spin_lock_irq(q->queue_lock);
+ if (blk_queue_stopped(q) && timer_pending(&q->unfreeze_timer))
+ /*
+ * Adding 1 in order to guarantee nonzero value until timer
+ * has actually expired.
+ */
+ seconds = jiffies_to_msecs(q->unfreeze_timer.expires
+ - jiffies) / 1000 + 1;
+ spin_unlock_irq(q->queue_lock);
+
+ return queue_var_show(seconds, (page));
+}
+
+/*
+ * When writing to the 'protect' attribute, input is the number of
+ * seconds to freeze the queue for. We call a helper function to park
+ * the heads and freeze/block the queue, then we make a block layer
+ * call to setup the thaw timeout. If input is 0, then the queue will
+ * be thawed by that helper function immediately.
+ */
+static ssize_t queue_protect_store(struct request_queue *q,
+ const char *page, size_t count)
+{
+ unsigned long seconds;
+
+ queue_var_store(&seconds, page, count);
+ blk_freeze_queue(q, seconds);
+
+ return count;
+}
+
static struct queue_sysfs_entry queue_requests_entry = {
.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
@@ -4110,12 +4245,19 @@ static struct queue_sysfs_entry queue_iosched_entry = {
.store = elv_iosched_store,
};
+static struct queue_sysfs_entry queue_protect_entry = {
+ .attr = { .name = "protect", .mode = S_IRUGO | S_IWUSR },
+ .show = queue_protect_show,
+ .store = queue_protect_store,
+};
+
static struct attribute *default_attrs[] = {
&queue_requests_entry.attr,
&queue_ra_entry.attr,
&queue_max_hw_sectors_entry.attr,
&queue_max_sectors_entry.attr,
&queue_iosched_entry.attr,
+ &queue_protect_entry.attr,
NULL,
};
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1854a69..082e2d3 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -385,6 +385,13 @@ struct request_queue
unsigned long unplug_delay; /* After this many jiffies */
struct work_struct unplug_work;
+ /*
+ * Auto-unfreeze state
+ */
+ struct timer_list unfreeze_timer;
+ int max_unfreeze; /* At most this many seconds */
+ struct work_struct unfreeze_work;
+
struct backing_dev_info backing_dev_info;
/*
