svn commit: r48681 - head/en_US.ISO8859-1/htdocs/news/status

Wed Apr 20 03:47:49 UTC 2016

Author: imp
Date: Wed Apr 20 03:47:47 2016
New Revision: 48681
URL: https://svnweb.freebsd.org/changeset/doc/48681

Log:
  Tweak wording in my I/O Schedule report

Modified:
  head/en_US.ISO8859-1/htdocs/news/status/report-2016-01-2016-03.xml

Modified: head/en_US.ISO8859-1/htdocs/news/status/report-2016-01-2016-03.xml
==============================================================================

--- head/en_US.ISO8859-1/htdocs/news/status/report-2016-01-2016-03.xml	Wed Apr 20 03:34:18 2016	(r48680)
+++ head/en_US.ISO8859-1/htdocs/news/status/report-2016-01-2016-03.xml	Wed Apr 20 03:47:47 2016	(r48681)
@@ -2548,23 +2548,41 @@
     <body>
       <p>An enhanced CAM I/O scheduler has been committed to the tree.
 	By default, this scheduler implements the old behavior.
-	However, a more adaptive scheduler can be enabled.  The more
-	adaptive scheduler allows pacing of different types of I/O to
-	allow the workload-preferred I/O to experience maximum
-	performance.  By measuring device response time at the lowest
-	levels, many artifacts of software queueing can be eliminated
-	and better performance can be achieved.  In addition, Queued
-	Trims are now supported for SATA devices that support them.
-	Details about the new scheduler are available in the
+	In addition, an advanced adaptive scheduler is available.
+	Along with the scheduler, SATA disks can now used Queued Trims
+	with devices that support them. Details about the new
+	scheduler are available in the
 	<a href="https://people.freebsd.org/~imp/bsdcan2015/iosched-v3.pdf">I/O Scheduling in FreeBSD's CAM Subsystem article (PDF)</a>
 	or from
 	<a href="https://www.youtube.com/watch?v=3WqOLolj5EU">the BSDCan 2015 talk</a>.</p>
 
-      <p>In essence, this I/O scheduler allows the user to choose
-	improved read performance by trading off some write
-	performance.  Or, if SSDs cannot garbage collect fast enough
-	to keep up with writes, to improve write performance at the
-	cost of some read performance.</p>
+      <p>In addition to the default scheduler, an advanced, adaptive I/O
+        scheduler is included. It is disabled by default, but can be enabled
+	with options CAM_ADAPTIVE_IOSCHED in your kernel config file. This
+	scheduler lets you favor reads over writes (or vice versa), control
+	the iops, bandwidth or concurrent operations (read, write, trim), and
+	lets you select static or dynamic control of these operations. In
+	addition, a number of statistics are collected for drive operations
+	that are published via sysctl. One advanced use for the adaptive I/O
+	scheduler is to compensate for deficiencies in some consumer-grade
+	SSDs. Some SSDs exhibit a performance cliff if you write too much data
+	to them too quickly due to internal garbage collection. Without the
+	I/O scheduler, read and write performance drop substantially once
+	garbage collection kicks in. The adaptive I/O scheduler can be
+	configured to monitor read latency. As read latency climbs, the I/O
+	schedulers reduces the allowed write throughput, within limits, to
+	attempt to maximize read performance. A simple use of the adaptive I/O
+	scheduler would be to limit write bandwidth, iops or concurrent
+        operations statically.</p>
+
+      <p>Future work on the I/O scheduler will be coupled with
+        improvements to the upper layers. The upper layers will be
+        enhanced to communicate how urgent I/O requests are. The I/O
+        scheduler will communicate how full the I/O queues are to the
+        upper layers so less urgent I/O can be submitted to the lower
+        layers as quickly as possible without overwhelming the lower
+        layers or starving other devices of requests.</p>
+
     </body>
 
     <sponsor>Netflix</sponsor>
