On 22.09.20 09:01, SeongJae Park wrote:
From: SeongJae Park <sjpark@xxxxxxxxx>
Persistent grants feature provides high scalability. On some small
systems, however, it could incur data copy overhead[1] and thus it is
required to be disabled. But, there is no option to disable it. For
the reason, this commit adds a module parameter for disabling of the
feature.
[1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability
Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>
Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
---
.../ABI/testing/sysfs-driver-xen-blkback | 8 ++++++++
drivers/block/xen-blkback/xenbus.c | 17 ++++++++++++++---
2 files changed, 22 insertions(+), 3 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback
index ecb7942ff146..0c42285c75ee 100644
--- a/Documentation/ABI/testing/sysfs-driver-xen-blkback
+++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback
@@ -35,3 +35,11 @@ Description:
controls the duration in milliseconds that blkback will not
cache any page not backed by a grant mapping.
The default is 10ms.
+
+What: /sys/module/xen_blkback/parameters/feature_persistent
+Date: September 2020
+KernelVersion: 5.10
+Contact: SeongJae Park <sjpark@xxxxxxxxx>
+Description:
+ Whether to enable the persistent grants feature or not.
+ The default is 1 (enable).
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index b9aa5d1ac10b..9c03d70469f4 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -879,6 +879,12 @@ static void reclaim_memory(struct xenbus_device *dev)
/* ** Connection ** */
+/* Enable the persistent grants feature. */
+static unsigned int feature_persistent = 1;
Use bool, please.
+module_param_named(feature_persistent, feature_persistent, int, 0644);
module_param()
+MODULE_PARM_DESC(feature_persistent,
+ "Enables the persistent grants feature");
+
/*
* Write the physical details regarding the block device to the store, and
* switch to Connected state.
@@ -906,7 +912,8 @@ static void connect(struct backend_info *be)
xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);
- err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", 1);
+ err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
+ feature_persistent ? 1 : 0);
Using bool above should allow to just use the value of
feature_persistent here.
Juergen
