From 18cab65b04dcb9c4b8da5517c91baaf1e395cbd0 Mon Sep 17 00:00:00 2001 From: Jakob Unterwurzacher Date: Sat, 27 Dec 2008 22:39:10 +0100 Subject: [PATCH] ionice: Extend the man page to explain the "none" class and cpu-nice inheritance Extend the ionice man page to explain the "none" class and how the cpu-nice => io-priority inheritance works. Signed-off-by: Jakob Unterwurzacher --- schedutils/ionice.1 | 29 ++++++++++++++++++----------- 1 file changed, 18 insertions(+), 11 deletions(-) diff --git a/schedutils/ionice.1 b/schedutils/ionice.1 index 93aabe82..3e8f97ba 100644 --- a/schedutils/ionice.1 +++ b/schedutils/ionice.1 @@ -6,25 +6,27 @@ ionice \- get/set program io scheduling class and priority [\fI-c\fR] \fI[-n\fR] [\fI-p\fR] [COMMAND [ARG...]] .SH DESCRIPTION -This program sets the io scheduling class and priority for a program. As of -this writing, Linux supports 3 scheduling classes: +This program sets or gets the io scheduling class and priority for a program. +If no arguments or just \fI-p\fR is given, \fIionice\fR will query the current +io scheduling class and priority for that process. -\fBIdle\fR. +As of this writing, a process can be in one of four scheduling classes: + +.IP "\fBIdle\fR" A program running with idle io priority will only get disk time when no other program has asked for disk io for a defined grace period. The impact of idle io processes on normal system activity should be zero. This scheduling class does not take a priority argument. Presently, this scheduling class is permitted for an ordinary user (since kernel 2.6.25). - -\fBBest effort\fR. -This is the default scheduling class for any process that hasn't asked for -a specific io priority. Programs inherit the CPU nice setting for io -priorities. This class takes a priority argument from \fI0-7\fR, with lower +.IP "\fBBest effort\fP" +This is the effective scheduling class for any process that hasn't asked for +a specific io priority. +This class takes a priority argument from \fI0-7\fR, with lower number being higher priority. Programs running at the same best effort priority are served in a round-robin fashion. -\fBReal time\fR. +.IP "\fBReal time\fR" The RT scheduling class is given first access to the disk, regardless of what else is going on in the system. Thus the RT class needs to be used with some care, as it can starve other processes. As with the best effort class, @@ -32,8 +34,13 @@ some care, as it can starve other processes. As with the best effort class, will receive on each scheduling window. This scheduling class is not permitted for an ordinary (i.e., non-root) user. -If no arguments or just \fI-p\fR is given, \fIionice\fR will query the -current io scheduling class and priority for that process. +.IP "\fBNone\fP" +A process that that hasn't asked for a specific io priority will formally be +in this class. The io scheduler will treat a process that is in this class as +if it were in the best effort class. The priority within the best effort +class will be dynamically derived from the cpu nice level of the process: +io_priority = (cpu_nice + 20) / 5 + .SH OPTIONS .LP -- 2.39.5