Date: Wed, 20 Apr 2016 03:47:47 +0000 (UTC) From: Warner Losh <imp@FreeBSD.org> To: doc-committers@freebsd.org, svn-doc-all@freebsd.org, svn-doc-head@freebsd.org Subject: svn commit: r48681 - head/en_US.ISO8859-1/htdocs/news/status Message-ID: <201604200347.u3K3llhm070832@repo.freebsd.org>
next in thread | raw e-mail | index | archive | help
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>
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201604200347.u3K3llhm070832>