From 8f67835f1e389978bb0809d5e528961986aa2a69 Mon Sep 17 00:00:00 2001
From: Martin Svec <martin.svec@zoner.cz>
Date: Tue, 15 Jan 2013 12:43:35 -0800
Subject: [PATCH] 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: Martin Svec<martin.svec@zoner.cz>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
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