This is a note to let you know that I've just added the patch titled
iscsi-target: Pre-allocate more tags to avoid ack starvation
to the 3.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
iscsi-target-pre-allocate-more-tags-to-avoid-ack-starvation.patch
and it can be found in the queue-3.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 4a4caa29f1abcb14377e05d57c0793d338fb945d Mon Sep 17 00:00:00 2001
From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Date: Fri, 10 Jan 2014 02:06:59 +0000
Subject: iscsi-target: Pre-allocate more tags to avoid ack starvation
From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
commit 4a4caa29f1abcb14377e05d57c0793d338fb945d upstream.
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.
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/target/iscsi/iscsi_target_nego.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- 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);
Patches currently in stable-queue which might be from nab@xxxxxxxxxxxxxxx are
queue-3.13/iscsi-target-pre-allocate-more-tags-to-avoid-ack-starvation.patch
queue-3.13/target-iscsi-fix-network-portal-creation-race.patch
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