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Subject[PATCH 08/10] xen/blkfront: negotiate hardware queue number with backend
Date
The max number of hardware queues for xen/blkfront is num_online_cpus() or set
by module parameter, while the number xen/blkback supported is notified through
xenstore("multi-queue-max-queues").
The negotiated number was the smaller one, and was written back to
xen/blkback as "multi-queue-num-queues".

Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
drivers/block/xen-blkfront.c | 71 ++++++++++++++++++++++++++++++++++++++++----
1 file changed, 66 insertions(+), 5 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index d551be0..32caf85 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -99,6 +99,10 @@ static unsigned int xen_blkif_max_segments = 32;
module_param_named(max, xen_blkif_max_segments, int, S_IRUGO);
MODULE_PARM_DESC(max, "Maximum amount of segments in indirect requests (default is 32)");

+static unsigned int xenblkif_max_queues;
+module_param_named(max_queues, xenblkif_max_queues, uint, 0644);
+MODULE_PARM_DESC(max_queues, "Maximum number of hardware queues per virtual disk");
+
#define BLK_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE)

/*
@@ -677,7 +681,7 @@ 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->nr_rings;
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;
@@ -1338,6 +1342,8 @@ static int talk_to_blkback(struct xenbus_device *dev,
struct xenbus_transaction xbt;
int err, i;
struct blkfront_ring_info *rinfo;
+ char *path;
+ size_t pathsize;

for (i = 0; i < info->nr_rings; i++) {
rinfo = &info->rinfo[i];
@@ -1354,6 +1360,13 @@ again:
goto out;
}

+ /* Write the number of queues */
+ err = xenbus_printf(xbt, dev->nodename, "multi-queue-num-queues", "%u", info->nr_rings);
+ if (err) {
+ message = "writing multi-queue-num-queues";
+ goto abort_transaction;
+ }
+
if (info->nr_rings == 1) {
rinfo = &info->rinfo[0];
err = xenbus_printf(xbt, dev->nodename,
@@ -1369,8 +1382,33 @@ again:
goto abort_transaction;
}
} else {
- /* Not supported at this stage */
- goto abort_transaction;
+ pathsize = strlen(dev->nodename) + 12;
+ path = kzalloc(pathsize, GFP_KERNEL);
+ if (!path) {
+ err = -ENOMEM;
+ message = "ENOMEM while writing ring references";
+ goto abort_transaction;
+ }
+ for (i = 0; i < info->nr_rings; i++) {
+ memset(path, 0, pathsize);
+ snprintf(path, pathsize, "%s/queue-%u", dev->nodename, i);
+
+ err = xenbus_printf(xbt, path,
+ "ring-ref", "%u", info->rinfo[i].ring_ref);
+ if (err) {
+ message = "writing ring-ref";
+ kfree(path);
+ goto abort_transaction;
+ }
+ err = xenbus_printf(xbt, path,
+ "event-channel", "%u", info->rinfo[i].evtchn);
+ if (err) {
+ message = "writing event-channel";
+ kfree(path);
+ goto abort_transaction;
+ }
+ }
+ kfree(path);
}
err = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
XEN_IO_PROTO_ABI_NATIVE);
@@ -1420,6 +1458,7 @@ static int blkfront_probe(struct xenbus_device *dev,
int err, vdevice, i, rindex;
struct blkfront_info *info;
struct blkfront_ring_info *rinfo;
+ unsigned int max_queues = 0;

/* FIXME: Use dynamic device id if this is not set. */
err = xenbus_scanf(XBT_NIL, dev->nodename,
@@ -1473,7 +1512,14 @@ static int blkfront_probe(struct xenbus_device *dev,
info->vdevice = vdevice;
info->connected = BLKIF_STATE_DISCONNECTED;

- info->nr_rings = 1;
+ /* Check if backend supports multiple queues */
+ err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+ "multi-queue-max-queues", "%u", &max_queues);
+ if (err < 0)
+ max_queues = 1;
+
+ info->nr_rings = min(max_queues, xenblkif_max_queues);
+ printk("xen/blkfront probe info->nr_rings:%d, backend support:%d\n", info->nr_rings, max_queues);
info->rinfo = kzalloc(sizeof(*rinfo) * info->nr_rings, GFP_KERNEL);
if (!info->rinfo) {
xenbus_dev_fatal(dev, -ENOMEM, "allocating ring_info structure");
@@ -1654,12 +1700,24 @@ static int blkif_recover(struct blkfront_info *info)
static int blkfront_resume(struct xenbus_device *dev)
{
struct blkfront_info *info = dev_get_drvdata(&dev->dev);
- int err;
+ int err = 0;
+ unsigned int max_queues = 0;

dev_dbg(&dev->dev, "blkfront_resume: %s\n", dev->nodename);

blkif_free(info, info->connected == BLKIF_STATE_CONNECTED);

+ err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+ "multi-queue-max-queues", "%u", &max_queues, NULL);
+ if (err)
+ max_queues = 1;
+
+ if (info->nr_rings != min(max_queues, xenblkif_max_queues)) {
+ /* At this stage, not support resume to a different hardware queue
+ * number */
+ return -1;
+ }
+
err = talk_to_blkback(dev, info);

/*
@@ -2165,6 +2223,9 @@ static int __init xlblk_init(void)
return -ENODEV;
}

+ /* Allow as many queues as there are CPUs, by default */
+ xenblkif_max_queues = num_online_cpus();
+
ret = xenbus_register_frontend(&blkfront_driver);
if (ret) {
unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
--
1.8.3.1


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