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Commit 8f67835f authored by Martin Svec's avatar Martin Svec Committed by Nicholas Bellinger
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target/rd: improve sg_table lookup scalability 



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: default avatarMartin <Svec&lt;martin.svec@zoner.cz>
Signed-off-by: default avatarNicholas Bellinger <nab@linux-iscsi.org>
parent d09816ae

drivers/target/target_core_rd.c

+4 −2
Original line number Diff line number Diff line
@@ -256,10 +256,12 @@ static void rd_free_device(struct se_device *dev) 


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;

	u32 i, sg_per_table = (RD_MAX_ALLOCATION_SIZE /

				sizeof(struct scatterlist));



	for (i = 0; i < rd_dev->sg_table_count; i++) {

	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))