xen-blkfront: Introduce a 'max' module parameter to alter the amount of indirect...

The max module parameter (by default 32) is the maximum number of
segments that the frontend will negotiate with the backend for indirect
descriptors.  Higher value means more potential throughput but more
memory usage. The backend picks the minimum of the frontend and its
default backend value.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkfront b/Documentation/ABI/testing/sysfs-driver-xen-blkfront
new file mode 100644 (file)
index 0000000..c0a6cb7
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-driver-xen-blkfront
@@ -0,0 +1,10 @@
+What:           /sys/module/xen_blkfront/parameters/max
+Date:           June 2013
+KernelVersion:  3.11
+Contact:        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
+Description:
+                Maximum number of segments that the frontend will negotiate
+                with the backend for indirect descriptors. The default value
+                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.

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index bac8cf31319b6b269840bd03583679c0cb4aec78..08bdfc3b2de2edc30fd3feb90dfc1ff6875d3091 100644 (file)
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -95,6 +95,8 @@ static const struct block_device_operations xlvbd_block_fops;
  */
 
 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)");
 
 #define BLK_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE)