iscsid: increase kernel thread nice

This sets the default xmit thread nice to -20. This will
increase throughput and decrease latency, but could hog
the cpu more. In the latter case you can set the nice in
/etc/iscsi/iscsid.conf's node.session.xmit_thread_priority setting.

1 files changed, 21 insertions, 0 deletions

diff --git a/etc/iscsid.conf b/etc/iscsid.conf
index 4f6e08a..686b3f9 100644
--- a/etc/iscsid.conf
+++ b/etc/iscsid.conf
@@ -146,6 +146,27 @@ node.session.cmds_max = 128
 # to a value between 1 and 128. The default is 32.
 node.session.queue_depth = 32
 
+##################################
+# MISC SYSTEM PERFORMANCE SETTINGS
+##################################
+
+# For software iscsi (iscsi_tcp) and iser (ib_iser) each session
+# has a thread used to transmit or queue data to the hardware. For
+# cxgb3i you will get a thread per host.
+#
+# Setting the thread's priority to a lower value can lead to higher throughput
+# and lower latencies. The lowest value is -20. Setting the priority to
+# a higher value, can lead to reduced IO performance, but if you are seeing
+# the iscsi or scsi threads dominate the use of the CPU then you may want
+# to set this value higher.
+#
+# Note: For cxgb3i you must set all sessions to the same value, or the
+# behavior is not defined.
+#
+# The default value is -20. The setting must be between -20 and 20.
+node.session.xmit_thread_priority = -20
+
+
 #***************
 # iSCSI settings
 #***************