svn commit: r48681 - head/en_US.ISO8859-1/htdocs/news/status
Warner Losh <[email protected]>
| Newsgroups | gmane.os.freebsd.devel.cvs.doc |
|---|---|
| Message-ID | <[email protected]> |
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>
_______________________________________________
[email protected] mailing list
https://lists.freebsd.org/mailman/listinfo/svn-doc-all
To unsubscribe, send any mail to "[email protected]"