Hi Martin,
On Fri, 2012-12-28 at 15:53 +0100, Martin Svec wrote:
> 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>
> ---
Apologies for taking so long to get back to this..
Applied to target-pending/for-next, but note for future reference that I
ended up having to apply this manually as your original patch appears to
be white-space mangled.
Aside from that minor bit, nice work on this optimization. ;)
--nab
> 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))
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