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Subject[PATCH 09/10] xen/blkback: get hardware queue number from blkfront
Date
Backend advertise the max number it supported to "multi-queue-max-queues", and
read the negotiate value from "multi-queue-num-queues".

Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
drivers/block/xen-blkback/blkback.c | 8 ++++++++
drivers/block/xen-blkback/xenbus.c | 36 ++++++++++++++++++++++++++++++------
2 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 0969e7e..34d72b0 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -80,6 +80,11 @@ module_param_named(max_persistent_grants, xen_blkif_max_pgrants, int, 0644);
MODULE_PARM_DESC(max_persistent_grants,
"Maximum number of grants to map persistently");

+unsigned int xenblk_max_queues;
+module_param_named(max_queues, xenblk_max_queues, uint, 0644);
+MODULE_PARM_DESC(max_queues,
+ "Maximum number of hardware queues per virtual disk");
+
/*
* The LRU mechanism to clean the lists of persistent grants needs to
* be executed periodically. The time interval between consecutive executions
@@ -1390,6 +1395,9 @@ static int __init xen_blkif_init(void)
if (!xen_domain())
return -ENODEV;

+ /* Allow as many queues as there are CPUs, by default */
+ xenblk_max_queues = num_online_cpus();
+
rc = xen_blkif_interface_init();
if (rc)
goto failed_init;
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 93e5f38..c33d8c9 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -21,6 +21,8 @@
#include <xen/grant_table.h>
#include "common.h"

+extern unsigned int xenblk_max_queues;
+
struct backend_info {
struct xenbus_device *dev;
struct xen_blkif *blkif;
@@ -225,12 +227,6 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
atomic_set(&blkif->drain, 0);
INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);

- blkif->nr_rings = 1;
- if (xen_blkif_alloc_rings(blkif)) {
- kmem_cache_free(xen_blkif_cachep, blkif);
- return ERR_PTR(-ENOMEM);
- }
-
return blkif;
}

@@ -647,6 +643,14 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
goto fail;
}

+ /* Multi-queue support: This is an optional feature. */
+ err = xenbus_printf(XBT_NIL, dev->nodename,
+ "multi-queue-max-queues", "%u", xenblk_max_queues);
+ if (err) {
+ pr_debug("Error writing multi-queue-num-queues\n");
+ goto fail;
+ }
+
/* setup back pointer */
be->blkif->be = be;

@@ -927,6 +931,7 @@ static int connect_ring(struct backend_info *be)
char *xspath;
size_t xspathsize;
const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-NNN" */
+ unsigned int requested_num_queues = 0;

DPRINTK("%s", dev->otherend);

@@ -954,6 +959,25 @@ static int connect_ring(struct backend_info *be)
be->blkif->vbd.feature_gnt_persistent = pers_grants;
be->blkif->vbd.overflow_max_grants = 0;

+ /*
+ * Read the number of hardware queus from frontend.
+ */
+ err = xenbus_scanf(XBT_NIL, dev->otherend, "multi-queue-num-queues", "%u", &requested_num_queues);
+ if (err < 0) {
+ requested_num_queues = 1;
+ } else {
+ if (requested_num_queues > xenblk_max_queues) {
+ /* buggy or malicious guest */
+ xenbus_dev_fatal(dev, err,
+ "guest requested %u queues, exceeding the maximum of %u.",
+ requested_num_queues, xenblk_max_queues);
+ return -1;
+ }
+ }
+ be->blkif->nr_rings = requested_num_queues;
+ if (xen_blkif_alloc_rings(be->blkif))
+ return -ENOMEM;
+
if (be->blkif->nr_rings == 1) {
err = xenbus_gather(XBT_NIL, dev->otherend, "ring-ref", "%lu",
&ring_ref, "event-channel", "%u", &evtchn, NULL);
--
1.8.3.1


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