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From: Colin Percival <cperciva@FreeBSD.org>
Date: Thu, 30 Jul 2015 04:01:01 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r286063 - head/release/tools
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Author: cperciva
Date: Thu Jul 30 04:01:00 2015
New Revision: 286063
URL: https://svnweb.freebsd.org/changeset/base/286063

Log:
  Disable blkif indirect segment I/Os in EC2 by default due to performance
  issues on some EC2 instance types.  Users may want to experiment with
  removing this from loader.conf and measuring the performance impact on
  the EC2 instances they are using.

Modified:
  head/release/tools/ec2.conf

Modified: head/release/tools/ec2.conf
==============================================================================
--- head/release/tools/ec2.conf	Thu Jul 30 03:50:01 2015	(r286062)
+++ head/release/tools/ec2.conf	Thu Jul 30 04:01:00 2015	(r286063)
@@ -70,6 +70,11 @@ vm_extra_pre_umount() {
 	# nodes, but apply the workaround just in case.
 	echo 'hw.broken_txfifo="1"' >> ${DESTDIR}/boot/loader.conf
 
+	# Some EC2 instances suffer a significant (~40%) reduction in
+	# throughput when using blkif indirect segment I/Os.  Disable this
+	# by default for now.
+	echo 'hw.xbd.xbd_enable_indirect="0"' >> ${DESTDIR}/boot/loader.conf
+
 	# The first time the AMI boots, the installed "first boot" scripts
 	# should be allowed to run:
 	# * ec2_configinit (download and process EC2 user-data)