This will enable changing the virtual boundary of null blk devices. For
now, null blk devices didn't have any restriction on the scatter/gather
elements received from the block layer. Add a module parameter that will
control the virtual boundary. This will enable testing the efficiency of
the block layer bounce buffer in case a suitable application will send
discontiguous IO to the given device.
Initial testing with patched FIO showed the following results (64 jobs,
128 iodepth):
IO size READ (virt=false) READ (virt=true) Write (virt=false) Write (virt=true)
---------- ------------------- ----------------- ------------------- -------------------
1k 10.7M 8482k 10.8M 8471k
2k 10.4M 8266k 10.4M 8271k
4k 10.4M 8274k 10.3M 8226k
8k 10.2M 8131k 9800k 7933k
16k 9567k 7764k 8081k 6828k
32k 8865k 7309k 5570k 5153k
64k 7695k 6586k 2682k 2617k
128k 5346k 5489k 1320k 1296k
Signed-off-by: Max Gurtovoy <mgurtovoy@xxxxxxxxxx>
---
drivers/block/null_blk/main.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index d6c821d48090..9ca80e38f7e5 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -84,6 +84,10 @@ enum {
NULL_Q_MQ = 2,
};
+static bool g_virt_boundary = false;
+module_param_named(virt_boundary, g_virt_boundary, bool, 0444);
+MODULE_PARM_DESC(virt_boundary, "Require a virtual boundary for the device. Default: False");
+
static int g_no_sched;
module_param_named(no_sched, g_no_sched, int, 0444);
MODULE_PARM_DESC(no_sched, "No io scheduler");
@@ -1880,6 +1884,9 @@ static int null_add_dev(struct nullb_device *dev)
BLK_DEF_MAX_SECTORS);
blk_queue_max_hw_sectors(nullb->q, dev->max_sectors);
+ if (g_virt_boundary)
+ blk_queue_virt_boundary(nullb->q, PAGE_SIZE - 1);
+
null_config_discard(nullb);
sprintf(nullb->disk_name, "nullb%d", nullb->index);
--
2.18.1
