Message-Id: <1469589685-31630-1-git-send-email-bob.liu@oracle.com>
Date:	Wed, 27 Jul 2016 11:21:25 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	linux-kernel@...r.kernel.org
Cc:	xen-devel@...ts.xenproject.org, konrad.wilk@...cle.com,
	roger.pau@...rix.com, Bob Liu <bob.liu@...cle.com>
Subject: [PATCH v3] xen-blkfront: dynamic configuration of per-vbd resources

The current VBD layer reserves buffer space for each attached device based on
three statically configured settings which are read at boot time.
 * max_indirect_segs: Maximum amount of segments.
 * max_ring_page_order: Maximum order of pages to be used for the shared ring.
 * max_queues: Maximum of queues(rings) to be used.

But the storage backend, workload, and guest memory result in very different
tuning requirements. It's impossible to centrally predict application
characteristics so it's best to leave allow the settings can be dynamiclly
adjusted based on workload inside the Guest.

Usage:
Show current values:
cat /sys/devices/vbd-xxx/max_indirect_segs
cat /sys/devices/vbd-xxx/max_ring_page_order
cat /sys/devices/vbd-xxx/max_queues

Write new values:
echo <new value> > /sys/devices/vbd-xxx/max_indirect_segs
echo <new value> > /sys/devices/vbd-xxx/max_ring_page_order
echo <new value> > /sys/devices/vbd-xxx/max_queues

Signed-off-by: Bob Liu <bob.liu@...cle.com>
--
v3:
 * Remove new_max_indirect_segments.
 * Fix BUG_ON().
v2:
 * Rename to max_ring_page_order.
 * Remove the waiting code suggested by Roger.
---
 drivers/block/xen-blkfront.c |  277 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 269 insertions(+), 8 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 1b4c380..57baa54 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -212,6 +212,10 @@ struct blkfront_info
 	/* Save uncomplete reqs and bios for migration. */
 	struct list_head requests;
 	struct bio_list bio_list;
+	/* For dynamic configuration. */
+	unsigned int reconfiguring:1;
+	unsigned int max_ring_page_order;
+	unsigned int max_queues;
 };
 
 static unsigned int nr_minors;
@@ -1350,6 +1354,31 @@ static void blkif_free(struct blkfront_info *info, int suspend)
 	for (i = 0; i < info->nr_rings; i++)
 		blkif_free_ring(&info->rinfo[i]);
 
+	/* Remove old xenstore nodes. */
+	if (info->nr_ring_pages > 1)
+		xenbus_rm(XBT_NIL, info->xbdev->nodename, "ring-page-order");
+
+	if (info->nr_rings == 1) {
+		if (info->nr_ring_pages == 1) {
+			xenbus_rm(XBT_NIL, info->xbdev->nodename, "ring-ref");
+		} else {
+			for (i = 0; i < info->nr_ring_pages; i++) {
+				char ring_ref_name[RINGREF_NAME_LEN];
+
+				snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
+				xenbus_rm(XBT_NIL, info->xbdev->nodename, ring_ref_name);
+			}
+		}
+	} else {
+		xenbus_rm(XBT_NIL, info->xbdev->nodename, "multi-queue-num-queues");
+
+		for (i = 0; i < info->nr_rings; i++) {
+			char queuename[QUEUE_NAME_LEN];
+
+			snprintf(queuename, QUEUE_NAME_LEN, "queue-%u", i);
+			xenbus_rm(XBT_NIL, info->xbdev->nodename, queuename);
+		}
+	}
 	kfree(info->rinfo);
 	info->rinfo = NULL;
 	info->nr_rings = 0;
@@ -1763,15 +1792,20 @@ static int talk_to_blkback(struct xenbus_device *dev,
 	const char *message = NULL;
 	struct xenbus_transaction xbt;
 	int err;
-	unsigned int i, max_page_order = 0;
+	unsigned int i, backend_max_order = 0;
 	unsigned int ring_page_order = 0;
 
 	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
-			   "max-ring-page-order", "%u", &max_page_order);
+			   "max-ring-page-order", "%u", &backend_max_order);
 	if (err != 1)
 		info->nr_ring_pages = 1;
 	else {
-		ring_page_order = min(xen_blkif_max_ring_order, max_page_order);
+		if (info->max_ring_page_order)
+			/* Dynamic configured through /sys. */
+			ring_page_order = min(info->max_ring_page_order, backend_max_order);
+		else
+			/* Default. */
+			ring_page_order = min(xen_blkif_max_ring_order, backend_max_order);
 		info->nr_ring_pages = 1 << ring_page_order;
 	}
 
@@ -1894,7 +1928,13 @@ static int negotiate_mq(struct blkfront_info *info)
 	if (err < 0)
 		backend_max_queues = 1;
 
-	info->nr_rings = min(backend_max_queues, xen_blkif_max_queues);
+	if (info->max_queues)
+		/* Dynamic configured through /sys */
+		info->nr_rings = min(backend_max_queues, info->max_queues);
+	else
+		/* Default. */
+		info->nr_rings = min(backend_max_queues, xen_blkif_max_queues);
+
 	/* We need at least one ring. */
 	if (!info->nr_rings)
 		info->nr_rings = 1;
@@ -2352,11 +2392,198 @@ static void blkfront_gather_backend_features(struct blkfront_info *info)
 			    NULL);
 	if (err)
 		info->max_indirect_segments = 0;
-	else
-		info->max_indirect_segments = min(indirect_segments,
-						  xen_blkif_max_segments);
+	else {
+		if (info->max_indirect_segments)
+			/* Dynamic configured through /sys */
+			info->max_indirect_segments = min(indirect_segments,
+							  info->max_indirect_segments);
+		else
+			info->max_indirect_segments = min(indirect_segments,
+							  xen_blkif_max_segments);
+	}
+}
+
+static ssize_t max_ring_page_order_show(struct device *dev,
+					struct device_attribute *attr, char *page)
+{
+	struct blkfront_info *info = dev_get_drvdata(dev);
+
+	return sprintf(page, "%u\n", get_order(info->nr_ring_pages * XEN_PAGE_SIZE));
+}
+
+static ssize_t max_indirect_segs_show(struct device *dev,
+				      struct device_attribute *attr, char *page)
+{
+	struct blkfront_info *info = dev_get_drvdata(dev);
+
+	return sprintf(page, "%u\n", info->max_indirect_segments);
+}
+
+static ssize_t max_queues_show(struct device *dev,
+			       struct device_attribute *attr, char *page)
+{
+	struct blkfront_info *info = dev_get_drvdata(dev);
+
+	return sprintf(page, "%u\n", info->nr_rings);
+}
+
+static ssize_t dynamic_reconfig_device(struct blkfront_info *info, ssize_t count)
+{
+	/*
+	 * Prevent new requests even to software request queue.
+	 */
+	blk_mq_freeze_queue(info->rq);
+
+	/*
+	 * Guarantee no uncompleted reqs.
+	 */
+	if (part_in_flight(&info->gd->part0) || info->reconfiguring) {
+		blk_mq_unfreeze_queue(info->rq);
+		pr_err("Dev:%s busy, please retry later.\n", dev_name(&info->xbdev->dev));
+		return -EBUSY;
+	}
+
+	/*
+	 * Frontend: 				Backend:
+	 * Freeze_queue()
+	 * Switch to XenbusStateClosed
+	 *					frontend_changed(StateClosed)
+	 *						> xen_blkif_disconnect()
+	 *						> Switch to XenbusStateClosed
+	 * blkback_changed(StateClosed)
+	 *	> blkfront_resume()
+	 *	> Switch to StateInitialised
+	 *					frontend_changed(StateInitialised):
+	 *						> reconnect
+	 *						> Switch to StateConnected
+	 * blkback_changed(StateConnected)
+	 *	> blkif_recover()
+	 *		> Also switch to StateConnected
+	 *		> Unfreeze_queue()
+	 */
+	info->reconfiguring = true;
+	xenbus_switch_state(info->xbdev, XenbusStateClosed);
+
+	return count;
+}
+
+static ssize_t max_indirect_segs_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	ssize_t ret;
+	unsigned int max_segs = 0, backend_max_segs = 0;
+	struct blkfront_info *info = dev_get_drvdata(dev);
+	int err;
+
+	ret = kstrtouint(buf, 10, &max_segs);
+	if (ret < 0)
+		return ret;
+
+	if (max_segs == info->max_indirect_segments)
+		return count;
+
+	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+			    "feature-max-indirect-segments", "%u", &backend_max_segs,
+			    NULL);
+	if (err) {
+		pr_err("Backend %s doesn't support feature-indirect-segments.\n",
+			info->xbdev->otherend);
+		return -EOPNOTSUPP;
+	}
+
+	if (max_segs > backend_max_segs) {
+		pr_err("Invalid max indirect segment (%u), backend-max: %u.\n",
+			max_segs, backend_max_segs);
+		return -EINVAL;
+	}
+
+	info->max_indirect_segments = max_segs;
+
+	return dynamic_reconfig_device(info, count);
+}
+
+static ssize_t max_ring_page_order_store(struct device *dev,
+				 struct device_attribute *attr,
+				 const char *buf, size_t count)
+{
+	ssize_t ret;
+	unsigned int max_order = 0, backend_max_order = 0;
+	struct blkfront_info *info = dev_get_drvdata(dev);
+	int err;
+
+	ret = kstrtouint(buf, 10, &max_order);
+	if (ret < 0)
+		return ret;
+
+	if ((1 << max_order) == info->nr_ring_pages)
+		return count;
+
+	if (max_order > XENBUS_MAX_RING_GRANT_ORDER) {
+		pr_err("Invalid max_ring_page_order (%u), max: %u.\n",
+				max_order, XENBUS_MAX_RING_GRANT_ORDER);
+		return -EINVAL;
+	}
+
+	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+			   "max-ring-page-order", "%u", &backend_max_order);
+	if (err != 1) {
+		pr_err("Backend %s doesn't support feature multi-page-ring.\n",
+			info->xbdev->otherend);
+		return -EOPNOTSUPP;
+	}
+	if (max_order > backend_max_order) {
+		pr_err("Invalid max_ring_page_order (%u), backend supports max: %u.\n",
+			max_order, backend_max_order);
+		return -EINVAL;
+	}
+	info->max_ring_page_order = max_order;
+
+	return dynamic_reconfig_device(info, count);
+}
+
+static ssize_t max_queues_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	ssize_t ret;
+	unsigned int max_queues = 0, backend_max_queues = 0;
+	struct blkfront_info *info = dev_get_drvdata(dev);
+	int err;
+
+	ret = kstrtouint(buf, 10, &max_queues);
+	if (ret < 0)
+		return ret;
+
+	if (max_queues == info->nr_rings)
+		return count;
+
+	if (max_queues > num_online_cpus()) {
+		pr_err("Invalid max_queues (%u), can't bigger than online cpus: %u.\n",
+			max_queues, num_online_cpus());
+		return -EINVAL;
+	}
+
+	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+			   "multi-queue-max-queues", "%u", &backend_max_queues);
+	if (err != 1) {
+		pr_err("Backend %s doesn't support block multi queue.\n",
+			info->xbdev->otherend);
+		return -EOPNOTSUPP;
+	}
+	if (max_queues > backend_max_queues) {
+		pr_err("Invalid max_queues (%u), backend supports max: %u.\n",
+			max_queues, backend_max_queues);
+		return -EINVAL;
+	}
+	info->max_queues = max_queues;
+
+	return dynamic_reconfig_device(info, count);
 }
 
+static DEVICE_ATTR_RW(max_queues);
+static DEVICE_ATTR_RW(max_ring_page_order);
+static DEVICE_ATTR_RW(max_indirect_segs);
+
 /*
  * Invoked when the backend is finally 'ready' (and has told produced
  * the details about the physical device - #sectors, size, etc).
@@ -2393,6 +2620,10 @@ static void blkfront_connect(struct blkfront_info *info)
 		 * supports indirect descriptors, and how many.
 		 */
 		blkif_recover(info);
+		if (info->reconfiguring) {
+			blk_mq_unfreeze_queue(info->rq);
+			info->reconfiguring = false;
+		}
 		return;
 
 	default:
@@ -2443,6 +2674,22 @@ static void blkfront_connect(struct blkfront_info *info)
 		return;
 	}
 
+	err = device_create_file(&info->xbdev->dev, &dev_attr_max_ring_page_order);
+	if (err)
+		goto fail;
+
+	err = device_create_file(&info->xbdev->dev, &dev_attr_max_indirect_segs);
+	if (err) {
+		device_remove_file(&info->xbdev->dev, &dev_attr_max_ring_page_order);
+		goto fail;
+	}
+
+	err = device_create_file(&info->xbdev->dev, &dev_attr_max_queues);
+	if (err) {
+		device_remove_file(&info->xbdev->dev, &dev_attr_max_ring_page_order);
+		device_remove_file(&info->xbdev->dev, &dev_attr_max_indirect_segs);
+		goto fail;
+	}
 	xenbus_switch_state(info->xbdev, XenbusStateConnected);
 
 	/* Kick pending requests. */
@@ -2453,6 +2700,12 @@ static void blkfront_connect(struct blkfront_info *info)
 	add_disk(info->gd);
 
 	info->is_ready = 1;
+	return;
+
+fail:
+	blkif_free(info, 0);
+	xlvbd_release_gendisk(info);
+	return;
 }
 
 /**
@@ -2500,8 +2753,16 @@ static void blkback_changed(struct xenbus_device *dev,
 		break;
 
 	case XenbusStateClosed:
-		if (dev->state == XenbusStateClosed)
+		if (dev->state == XenbusStateClosed) {
+			if (info->reconfiguring)
+				if (blkfront_resume(info->xbdev)) {
+					/* Resume failed. */
+					info->reconfiguring = false;
+					xenbus_switch_state(info->xbdev, XenbusStateClosed);
+					pr_err("Resume from dynamic configuration failed\n");
+				}
 			break;
+		}
 		/* Missed the backend's Closing state -- fallthrough */
 	case XenbusStateClosing:
 		if (info)
-- 
1.7.10.4

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