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authorNicholas Bellinger <nab@linux-iscsi.org>2014-01-10 02:06:59 +0000
committerNicholas Bellinger <nab@linux-iscsi.org>2014-01-19 10:59:05 +0000
commit4a4caa29f1abcb14377e05d57c0793d338fb945d (patch)
tree9aa82f238da7f6dc93d543aa76616bafdfbf552b /drivers/target/iscsi
parent49a47f2cafbe4ca3839f8ae99c6fdeffd5fcaf45 (diff)
iscsi-target: Pre-allocate more tags to avoid ack starvation
This patch addresses an traditional iscsi-target fabric ack starvation issue where iscsit_allocate_cmd() -> percpu_ida_alloc_state() ends up hitting slow path percpu-ida code, because iscsit_ack_from_expstatsn() is expected to free ack'ed tags after tag allocation. This is done to take into account the tags waiting to be acknowledged and released in iscsit_ack_from_expstatsn(), but who's number are not directly limited by the CmdSN Window queue_depth being enforced by the target. So that said, this patch bumps up the pre-allocated number of per session tags to: (max(queue_depth, ISCSIT_MIN_TAGS) * 2) + ISCSIT_EXTRA_TAGS for good measure to avoid the percpu_ida_alloc_state() slow path. Cc: <stable@vger.kernel.org> #3.12+ Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Diffstat (limited to 'drivers/target/iscsi')
-rw-r--r--drivers/target/iscsi/iscsi_target_nego.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/target/iscsi/iscsi_target_nego.c b/drivers/target/iscsi/iscsi_target_nego.c
index 83c965c6538..582ba84075e 100644
--- a/drivers/target/iscsi/iscsi_target_nego.c
+++ b/drivers/target/iscsi/iscsi_target_nego.c
@@ -1192,7 +1192,7 @@ get_target:
*/
alloc_tags:
tag_num = max_t(u32, ISCSIT_MIN_TAGS, queue_depth);
- tag_num += (tag_num / 2) + ISCSIT_EXTRA_TAGS;
+ tag_num = (tag_num * 2) + ISCSIT_EXTRA_TAGS;
tag_size = sizeof(struct iscsi_cmd) + conn->conn_transport->priv_size;
ret = transport_alloc_session_tags(sess->se_sess, tag_num, tag_size);