From: SeongJae Park <[email protected]>
Persistent grants feature provides high scalability. On some small
systems, however, it could incur data copy overheads[1] and thus it is
required to be disabled. It can be disabled from blkback side using a
module parameter, 'feature_persistent'. But, it is impossible from
blkfront side. For the reason, this commit adds a blkfront module
parameter for disabling of the feature.
[1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability
Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Acked-by: Roger Pau Monné <[email protected]>
---
.../ABI/testing/sysfs-driver-xen-blkfront | 9 +++++++++
drivers/block/xen-blkfront.c | 20 ++++++++++++++-----
2 files changed, 24 insertions(+), 5 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkfront b/Documentation/ABI/testing/sysfs-driver-xen-blkfront
index c0a6cb7eb314..9c31334cb2e6 100644
--- a/Documentation/ABI/testing/sysfs-driver-xen-blkfront
+++ b/Documentation/ABI/testing/sysfs-driver-xen-blkfront
@@ -8,3 +8,12 @@ Description:
is 32 - higher value means more potential throughput but more
memory usage. The backend picks the minimum of the frontend
and its default backend value.
+
+What: /sys/module/xen_blkfront/parameters/feature_persistent
+Date: September 2020
+KernelVersion: 5.10
+Contact: SeongJae Park <[email protected]>
+Description:
+ Whether to enable the persistent grants feature or not. Note
+ that this option only takes effect on newly created frontends.
+ The default is Y (enable).
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 91de2e0755ae..48629d3433b4 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1866,8 +1866,8 @@ static int talk_to_blkback(struct xenbus_device *dev,
message = "writing protocol";
goto abort_transaction;
}
- err = xenbus_printf(xbt, dev->nodename,
- "feature-persistent", "%u", 1);
+ err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
+ info->feature_persistent);
if (err)
dev_warn(&dev->dev,
"writing persistent grants feature to xenbus");
@@ -1941,6 +1941,13 @@ static int negotiate_mq(struct blkfront_info *info)
}
return 0;
}
+
+/* Enable the persistent grants feature. */
+static bool feature_persistent = true;
+module_param(feature_persistent, bool, 0644);
+MODULE_PARM_DESC(feature_persistent,
+ "Enables the persistent grants feature");
+
/**
* 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
@@ -2007,6 +2014,8 @@ static int blkfront_probe(struct xenbus_device *dev,
info->vdevice = vdevice;
info->connected = BLKIF_STATE_DISCONNECTED;
+ info->feature_persistent = feature_persistent;
+
/* Front end dir is a number, which is used as the id. */
info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
dev_set_drvdata(&dev->dev, info);
@@ -2316,9 +2325,10 @@ static void blkfront_gather_backend_features(struct blkfront_info *info)
if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0))
blkfront_setup_discard(info);
- info->feature_persistent =
- !!xenbus_read_unsigned(info->xbdev->otherend,
- "feature-persistent", 0);
+ if (info->feature_persistent)
+ info->feature_persistent =
+ !!xenbus_read_unsigned(info->xbdev->otherend,
+ "feature-persistent", 0);
indirect_segments = xenbus_read_unsigned(info->xbdev->otherend,
"feature-max-indirect-segments", 0);
--
2.17.1