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Date: Fri, 12 Sep 2014 01:57:22 +0200
From: Arianna Avanzini <avanzini.arianna@...il.com>
To: konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
david.vrabel@...rix.com, xen-devel@...ts.xenproject.org,
linux-kernel@...r.kernel.org
Cc: hch@...radead.org, bob.liu@...cle.com, felipe.franciosi@...rix.com,
axboe@...com, avanzini.arianna@...il.com
Subject: [PATCH RFC v2 3/5] xen, blkfront: negotiate the number of block rings with the backend
This commit implements the negotiation of the number of block rings
to be used; as a default, the number of rings is decided by the
frontend driver and is equal to the number of hardware queues that
the backend makes available. In case of guest migration towards a
host whose devices expose a different number of hardware queues, the
number of I/O rings used by the frontend driver remains the same;
XenStore keys may vary if the frontend needs to be compatible with
a host not having multi-queue support.
Signed-off-by: Arianna Avanzini <avanzini.arianna@...il.com>
---
drivers/block/xen-blkfront.c | 95 +++++++++++++++++++++++++++++++++++++++-----
1 file changed, 84 insertions(+), 11 deletions(-)
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 9282df1..77e311d 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -137,7 +137,7 @@ struct blkfront_info
int vdevice;
blkif_vdev_t handle;
enum blkif_state connected;
- unsigned int nr_rings;
+ unsigned int nr_rings, old_nr_rings;
struct blkfront_ring_info *rinfo;
struct request_queue *rq;
unsigned int feature_flush;
@@ -147,6 +147,7 @@ struct blkfront_info
unsigned int discard_granularity;
unsigned int discard_alignment;
unsigned int feature_persistent:1;
+ unsigned int hardware_queues;
unsigned int max_indirect_segments;
int is_ready;
/* Block layer tags. */
@@ -669,7 +670,7 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
memset(&info->tag_set, 0, sizeof(info->tag_set));
info->tag_set.ops = &blkfront_mq_ops;
- info->tag_set.nr_hw_queues = 1;
+ info->tag_set.nr_hw_queues = info->hardware_queues ? : 1;
info->tag_set.queue_depth = BLK_RING_SIZE;
info->tag_set.numa_node = NUMA_NO_NODE;
info->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
@@ -938,6 +939,7 @@ static void xlvbd_release_gendisk(struct blkfront_info *info)
info->gd = NULL;
}
+/* Must be called with io_lock held */
static void kick_pending_request_queues(struct blkfront_ring_info *rinfo,
unsigned long *flags)
{
@@ -1351,10 +1353,24 @@ again:
goto destroy_blkring;
}
+ /* Advertise the number of rings */
+ err = xenbus_printf(xbt, dev->nodename, "nr_blk_rings",
+ "%u", info->nr_rings);
+ if (err) {
+ xenbus_dev_fatal(dev, err, "advertising number of rings");
+ goto abort_transaction;
+ }
+
for (i = 0 ; i < info->nr_rings ; i++) {
- BUG_ON(i > 0);
- snprintf(ring_ref_s, 64, "ring-ref");
- snprintf(evtchn_s, 64, "event-channel");
+ if (!info->hardware_queues) {
+ BUG_ON(i > 0);
+ /* Support old XenStore keys */
+ snprintf(ring_ref_s, 64, "ring-ref");
+ snprintf(evtchn_s, 64, "event-channel");
+ } else {
+ snprintf(ring_ref_s, 64, "ring-ref-%d", i);
+ snprintf(evtchn_s, 64, "event-channel-%d", i);
+ }
err = xenbus_printf(xbt, dev->nodename,
ring_ref_s, "%u", info->rinfo[i].ring_ref);
if (err) {
@@ -1403,6 +1419,14 @@ again:
return err;
}
+static inline int blkfront_gather_hw_queues(struct blkfront_info *info,
+ unsigned int *nr_queues)
+{
+ return xenbus_gather(XBT_NIL, info->xbdev->otherend,
+ "nr_supported_hw_queues", "%u", nr_queues,
+ NULL);
+}
+
/**
* Entry point to this code when a new device is created. Allocate the basic
* structures and the ring buffer for communication with the backend, and
@@ -1414,6 +1438,7 @@ static int blkfront_probe(struct xenbus_device *dev,
{
int err, vdevice, i, r;
struct blkfront_info *info;
+ unsigned int nr_queues;
/* FIXME: Use dynamic device id if this is not set. */
err = xenbus_scanf(XBT_NIL, dev->nodename,
@@ -1472,10 +1497,19 @@ static int blkfront_probe(struct xenbus_device *dev,
info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
dev_set_drvdata(&dev->dev, info);
- /* Allocate the correct number of rings. */
- info->nr_rings = 1;
- pr_info("blkfront: %s: %d rings\n",
- info->gd->disk_name, info->nr_rings);
+ /* Gather the number of hardware queues as soon as possible */
+ err = blkfront_gather_hw_queues(info, &nr_queues);
+ if (err)
+ info->hardware_queues = 0;
+ else
+ info->hardware_queues = nr_queues;
+ /*
+ * The backend has told us the number of hw queues he wants.
+ * Allocate the correct number of rings.
+ */
+ info->nr_rings = info->hardware_queues ? : 1;
+ pr_info("blkfront: %s: %d hardware queues, %d rings\n",
+ info->gd->disk_name, info->hardware_queues, info->nr_rings);
info->rinfo = kzalloc(info->nr_rings *
sizeof(struct blkfront_ring_info),
@@ -1556,7 +1590,7 @@ static int blkif_recover(struct blkfront_info *info)
segs = blkfront_gather_indirect(info);
- for (r = 0 ; r < info->nr_rings ; r++) {
+ for (r = 0 ; r < info->old_nr_rings ; r++) {
rc |= blkif_setup_shadow(&info->rinfo[r], ©);
rc |= blkfront_setup_indirect(&info->rinfo[r], segs);
if (rc) {
@@ -1599,7 +1633,7 @@ static int blkif_recover(struct blkfront_info *info)
/* Now safe for us to use the shared ring */
info->connected = BLKIF_STATE_CONNECTED;
- for (i = 0 ; i < info->nr_rings ; i++) {
+ for (i = 0 ; i < info->old_nr_rings ; i++) {
spin_lock_irqsave(&info->rinfo[i].io_lock, flags);
/* Kick any other new requests queued since we resumed */
kick_pending_request_queues(&info->rinfo[i], &flags);
@@ -1659,11 +1693,46 @@ static int blkfront_resume(struct xenbus_device *dev)
{
struct blkfront_info *info = dev_get_drvdata(&dev->dev);
int err;
+ unsigned int nr_queues, prev_nr_queues;
+ bool mq_to_rq_transition;
dev_dbg(&dev->dev, "blkfront_resume: %s\n", dev->nodename);
+ prev_nr_queues = info->hardware_queues;
+
+ err = blkfront_gather_hw_queues(info, &nr_queues);
+ if (err < 0)
+ nr_queues = 0;
+ mq_to_rq_transition = prev_nr_queues && !nr_queues;
+
+ if (prev_nr_queues != nr_queues) {
+ printk(KERN_INFO "blkfront: %s: hw queues %u -> %u\n",
+ info->gd->disk_name, prev_nr_queues, nr_queues);
+ if (mq_to_rq_transition) {
+ struct blk_mq_hw_ctx *hctx;
+ unsigned int i;
+ /*
+ * Switch from multi-queue to single-queue:
+ * update hctx-to-ring mapping before
+ * resubmitting any requests
+ */
+ queue_for_each_hw_ctx(info->rq, hctx, i)
+ hctx->driver_data = &info->rinfo[0];
+ }
+ info->hardware_queues = nr_queues;
+ }
+
blkif_free(info, info->connected == BLKIF_STATE_CONNECTED);
+ /* Free with old number of rings, but rebuild with new */
+ info->old_nr_rings = info->nr_rings;
+ /*
+ * Must not update if transition didn't happen, we're keeping
+ * the old number of rings.
+ */
+ if (mq_to_rq_transition)
+ info->nr_rings = 1;
+
err = talk_to_blkback(dev, info);
/*
@@ -1863,6 +1932,10 @@ static void blkfront_connect(struct blkfront_info *info)
* supports indirect descriptors, and how many.
*/
blkif_recover(info);
+ info->rinfo = krealloc(info->rinfo,
+ info->nr_rings * sizeof(struct blkfront_ring_info),
+ GFP_KERNEL);
+
return;
default:
--
2.1.0
--
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