sched.7: Add a new introductory paragraph describing the nice value

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man7/sched.7 b/man7/sched.7
index cae43fe134fe1da89308ea3213fd2df22b4f78e4..c2ff00bbed0b0cee9ce83d8301097aa89b058d31 100644 (file)
--- a/man7/sched.7
+++ b/man7/sched.7
@@ -380,6 +380,19 @@ but denied to run by the scheduler.
 This ensures fair progress among all \fBSCHED_OTHER\fP threads.
 .\"
 .SS The nice value
+The nice value is a per-process attribute
+that can be used to influence the CPU scheduler to
+favor or disfavor a process in scheduling decisions.
+It affects the scheduling of
+.BR SCHED_OTHER
+and
+.BR SCHED_BATCH
+(see below)
+processes.
+According to POSIX.1, the threads in a process should share a nice value.
+However, on Linux, the nice value is a per-thread attribute:
+different threads in the same process may have different nice values.
+
 The range of the nice value
 varies across UNIX systems.
 On modern Linux, the range is \-20 (high priority) to +19 (low priority).