Date:	Sat, 4 Dec 2010 21:36:40 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] maximize dispatching in block throttle

On Fri, Dec 3, 2010 at 10:32 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> It should not be too hard. IO schedulers already create
> /sys/block/<dev>/queue/iosched/ dir and we can create <dev>/queue/throttle/
> dir and export throttle related tunables there.

Evening, Vivek.

I worked the framework for the tunable out.

If in right direction, I will complete it soon.

Thanks
Hillf



--- a/block/blk-throttle.c	2010-11-01 19:54:12.000000000 +0800
+++ b/block/blk-throttle.c	2010-12-04 21:24:58.000000000 +0800
@@ -98,6 +98,27 @@ struct throtl_data
 	struct delayed_work throtl_work;

 	atomic_t limits_changed;
+
+	/*
+	 * following is sysfs stuff about queue throttle
+	 */
+	struct kobject	kobj;
+
+	struct mutex	sysfs_lock;
+
+	/* Max dispatch from a group in 1 round */
+	int grp_quantum;
+
+	/* Total max dispatch from all groups in one round */
+	int q_quantum;
+
+	/* Throttling is performed over 100ms slice and after that
+	 * slice is renewed
+	 */
+	unsigned long time_slice;
+
+	/* read percentage of dispatch from a group in 1 round */
+	int read_percentage;
 };

 enum tg_state_flags {
@@ -644,11 +665,19 @@ static int throtl_dispatch_tg(struct thr
 				struct bio_list *bl)
 {
 	unsigned int nr_reads = 0, nr_writes = 0;
-	unsigned int max_nr_reads = throtl_grp_quantum*3/4;
-	unsigned int max_nr_writes = throtl_grp_quantum - nr_reads;
+	unsigned int max_nr_reads, max_nr_writes;
 	struct bio *bio;

-	/* Try to dispatch 75% READS and 25% WRITES */
+	max_nr_reads = td->read_percentage * td->grp_quantum /100;
+	if (! max_nr_reads)
+		max_nr_reads = 1;
+	/*
+	 * both are not computed stricktly here to throttle I/O
+	 */
+	if (max_nr_reads < td->grp_quantum)
+		max_nr_writes = td->grp_quantum - max_nr_reads;
+	else
+		max_nr_writes = 1;

 	while ((bio = bio_list_peek(&tg->bio_lists[READ]))
 		&& tg_may_dispatch(td, tg, bio, NULL)) {
@@ -1025,10 +1054,169 @@ out:
 	return 0;
 }

+/*
+ * sysfs stuff
+ */
+
+struct throttle_sysfs_entry {
+	struct attribute attr;
+	ssize_t (*show)(struct throtl_data *, char *);
+	ssize_t (*store)(struct throtl_data *, const char *, size_t);
+};
+
+static ssize_t
+throttle_show_time_slice(struct throtl_data *td, char *page)
+{
+	unsigned int msecs = jiffies_to_msecs(td->time_slice);
+	return sprintf(page, "%lu\n", msecs);
+}
+static ssize_t
+throttle_store_time_slice(struct throtl_data *td,
+				const char *page, size_t len)
+{
+	char *p = (char *) page;
+	unsigned long msecs = simple_strtoul(p, &p, 10);
+
+	td->time_slice = msecs_to_jiffies(msecs);
+	return len;
+}
+static struct throttle_sysfs_entry  throttle_time_slice_entry = {
+	.attr = { .name = "time_slice", .mode = S_IRUGO | S_IWUSR },
+	.show = throttle_show_time_slice,
+	.store = throttle_store_time_slice,
+};
+
+static ssize_t
+throttle_show_grp_quantum(struct throtl_data *td, char *page)
+{
+	return sprintf(page, "%d\n", td->grp_quantum);
+}
+static ssize_t
+throttle_store_grp_quantum(struct throtl_data *td,
+				const char *page, size_t len)
+{
+	char *p = (char *) page;
+	unsigned long v = simple_strtoul(p, &p, 10);
+
+	td->grp_quantum = (int) v;
+	return len;
+}
+static struct throttle_sysfs_entry  throttle_grp_quantum_entry = {
+	.attr = { .name = "grp_quantum", .mode = S_IRUGO | S_IWUSR },
+	.show = throttle_show_grp_quantum,
+	.store = throttle_store_grp_quantum,
+};
+
+static ssize_t
+throttle_show_q_quantum(struct throtl_data *td, char *page)
+{
+	return sprintf(page, "%d\n", td->q_quantum);
+}
+static ssize_t
+throttle_store_q_quantum(struct throtl_data *td,
+				const char *page, size_t len)
+{
+	char *p = (char *) page;
+	unsigned long v = simple_strtoul(p, &p, 10);
+
+	td->q_quantum = (int) v;
+	return len;
+}
+static struct throttle_sysfs_entry  throttle_q_quantum_entry = {
+	.attr = { .name = "q_quantum", .mode = S_IRUGO | S_IWUSR },
+	.show = throttle_show_q_quantum,
+	.store = throttle_store_q_quantum,
+};
+
+static ssize_t
+throttle_show_read_percentage(struct throtl_data *td, char *page)
+{
+	return sprintf(page, "%d\n", td->read_percentage);
+}
+static ssize_t
+throttle_store_read_percentage(struct throtl_data *td,
+				const char *page, size_t len)
+{
+	char *p = (char *) page;
+	unsigned long v = simple_strtoul(p, &p, 10);
+
+	if (v > 99)
+		v = 99;
+	else if (v < 1)
+		v = 1;
+	td->read_percentage = (int) v;
+	return len;
+}
+static struct throttle_sysfs_entry  throttle_read_percentage_entry = {
+	.attr = { .name = "read_percentage", .mode = S_IRUGO | S_IWUSR },
+	.show = throttle_show_read_percentage,
+	.store = throttle_store_read_percentage,
+};
+
+static struct attribute *throttle_attrs[] = {
+	&throttle_grp_quantum_entry.attr,
+	&throttle_q_quantum_entry.attr,
+	&throttle_time_slice_entry.attr,
+	&throttle_read_percentage_entry.attr,
+	NULL,
+};
+
+static ssize_t
+throttle_attr_store(struct kobject *kobj, struct attribute *attr,
+		    const char *page, size_t length)
+{
+	struct throttle_sysfs_entry *entry =
+		container_of(attr, struct throttle_sysfs_entry, attr);
+	struct throtl_data *td =
+		container_of(kobj, struct throtl_data, kobj);
+	ssize_t rtn;
+
+	if (! entry->store)
+		return -EIO;
+	mutex_lock(&td->sysfs_lock);
+	rtn = entry->store(td, page, length);
+	mutex_unlock(&td->sysfs_lock);
+	return rtn;
+}
+
+static ssize_t
+throttle_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
+{
+	struct throttle_sysfs_entry *entry =
+		container_of(attr, struct throttle_sysfs_entry, attr);
+	struct throtl_data *td =
+		container_of(kobj, struct throtl_data, kobj);
+	ssize_t rtn;
+
+	if (! entry->show)
+		return -EIO;
+	mutex_lock(&td->sysfs_lock);
+	rtn = entry->show(td, page);
+	mutex_unlock(&td->sysfs_lock);
+	return rtn;
+}
+
+static const struct sysfs_ops  throttle_sysfs_ops = {
+	.show	= throttle_attr_show,
+	.store	= throttle_attr_store,
+};
+
+static void throttle_release(struct kobject *kobj)
+{
+}
+
+static struct kobj_type blk_throttle_ktype = {
+	.sysfs_ops	= &throttle_sysfs_ops,
+	.default_attrs	= throttle_attrs,
+	.release	= throttle_release,
+};
+
+
 int blk_throtl_init(struct request_queue *q)
 {
 	struct throtl_data *td;
 	struct throtl_grp *tg;
+	int rtn;

 	td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
 	if (!td)
@@ -1049,6 +1237,20 @@ int blk_throtl_init(struct request_queue
 	tg->bps[0] = tg->bps[1] = -1;
 	tg->iops[0] = tg->iops[1] = -1;

+	mutex_init(&td->sysfs_lock);
+	td->grp_quantum = throtl_grp_quantum;
+	td->q_quantum = throtl_quantum;
+	td->time_slice = throtl_slice;
+	/* Try to dispatch 75% READS and 25% WRITES by default */
+	td->read_percentage = 75;
+	kobject_init(&td->kobj, &blk_throttle_ktype);
+	rtn = kobject_add(&td->kobj, kobject_get(&q->kobj), "%s", "throttle");
+	if (rtn < 0) {
+		kfree(td);
+		return rtn;
+	}
+	kobject_uevent(&td->kobj, KOBJ_ADD);
+
 	/*
 	 * Set root group reference to 2. One reference will be dropped when
 	 * all groups on tg_list are being deleted during queue exit. Other
@@ -1111,6 +1313,9 @@ void blk_throtl_exit(struct request_queu
 	 * it.
 	 */
 	throtl_shutdown_timer_wq(q);
+	kobject_uevent(&td->kobj, KOBJ_REMOVE);
+	kobject_del(&td->kobj);
+	kobject_put(&q->kobj);
 	throtl_td_free(td);
 }
--
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