Sequential scan of rd_dev->sg_table_array in rd_get_sg_table is
a serious I/O performance bottleneck for large rd LUNs. Fix this
by computing the sg_table index directly from page offset because
all sg_tables (except the last one) have the same number of pages.
Tested with 90 GiB rd_mcp LUN, where the patch improved maximal
random R/W IOPS by more than 100-150%, depending on actual
hardware and SAN setup.
Signed-off-by: Martin Svec<martin.svec@xxxxxxxx>
---
drivers/target/target_core_rd.c | 6 +++++-
1 files changed, 5 insertions(+), 1 deletions(-)
diff --git a/drivers/target/target_core_rd.c b/drivers/target/target_core_rd.c
index d00bbe3..549633b 100644
--- a/drivers/target/target_core_rd.c
+++ b/drivers/target/target_core_rd.c
@@ -271,7 +271,11 @@ static struct rd_dev_sg_table *rd_get_sg_table(struct rd_dev *rd_dev, u32 page)
u32 i;
struct rd_dev_sg_table *sg_table;
- for (i = 0; i< rd_dev->sg_table_count; i++) {
+ u32 sg_per_table = (RD_MAX_ALLOCATION_SIZE /
+ sizeof(struct scatterlist));
+
+ i = page / sg_per_table;
+ if (i< rd_dev->sg_table_count) {
sg_table =&rd_dev->sg_table_array[i];
if ((sg_table->page_start_offset<= page)&&
(sg_table->page_end_offset>= page))
--
1.7.8.6
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