From owner-svn-doc-all@freebsd.org Wed Apr 20 03:47:48 2016 Return-Path: Delivered-To: svn-doc-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id E34F7B157BD; Wed, 20 Apr 2016 03:47:48 +0000 (UTC) (envelope-from imp@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id BB454127E; Wed, 20 Apr 2016 03:47:48 +0000 (UTC) (envelope-from imp@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id u3K3llJe070833; Wed, 20 Apr 2016 03:47:47 GMT (envelope-from imp@FreeBSD.org) Received: (from imp@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id u3K3llhm070832; Wed, 20 Apr 2016 03:47:47 GMT (envelope-from imp@FreeBSD.org) Message-Id: <201604200347.u3K3llhm070832@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: imp set sender to imp@FreeBSD.org using -f From: Warner Losh Date: Wed, 20 Apr 2016 03:47:47 +0000 (UTC) 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 X-SVN-Group: doc-head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-doc-all@freebsd.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "SVN commit messages for the entire doc trees \(except for " user" , " projects" , and " translations" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 20 Apr 2016 03:47:49 -0000 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 @@

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 I/O Scheduling in FreeBSD's CAM Subsystem article (PDF) or from the BSDCan 2015 talk.

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.

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.

+ +

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.

+ Netflix