On Sat, Jan 17, 2009 at 02:38:32AM +0100, Jakob Unterwurzacher wrote:
> Allow users to set the "none" class on processes. Using the
You're right that the SYS_ioprio_get syscall differentiate between
"none" (0) and "best-effort" (2) classes, but in all documentation
are three classes only (and de facto we have three classes only).
I'm not sure with your previous patch to ionice.1 man page. Would be
better to describe the "none" as a subset of BE rather than any
separate class? I think the sentence "a process can be in one of four
scheduling classes" is not true, because we have three classes only.
The change to ionice.c makes sense, but the "none" should be more
carefully described in the man page. Please, see below my suggestion.
Karel
diff --git a/schedutils/ionice.1 b/schedutils/ionice.1
index aef40c3..a172832 100644
--- a/schedutils/ionice.1
+++ b/schedutils/ionice.1
@@ -11,7 +11,7 @@ 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.
-As of this writing, a process can be in one of four scheduling classes:
+As of this writing, a process can be in one of three scheduling classes:
.IP "\fBIdle\fP"
A program running with idle io priority will only get disk time when no other
@@ -27,6 +27,14 @@ 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.
+The ionice(1) command and SYS_ioprio_* syscalls differentiate between processes
+that hasn't asked for io priority and processes that has asked for io priority.
+The processes that hasn't asked for io priority formally use "\fBnone\fP" as a
+scheduling class, but the io scheduler will treat such processes 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.
+
.IP "\fBReal time\fP"
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
@@ -35,12 +43,6 @@ 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.
-.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
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