new man page for the kernel process scheduler

Reference: /n/atom/patch/applied/schedman
Date: Sun Jun  8 13:04:01 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/man/9/sched	Thu Jan  1 00:00:00 1970
+++ /sys/man/9/sched	Sun Jun  8 13:03:59 2014
@@ -0,0 +1,109 @@
+.TH SCHED 9
+.SH NAME
+anyhigher, anyready, hzsched, procpriority, procrestore, procsaved, procsave, scheddump, schedinit, schedstats, sched, yield \- scheduler interactions
+.SH SYNOPSIS
+.ta \w'\fLvoid 'u
+.B
+int	anyhigher(void)
+.PP
+.B
+int	anyready(void)
+.PP
+.B
+void	hzsched(void);
+.PP
+.B
+void	procpriority(Proc *p, int priority, int fixed)
+.PP
+.B
+void	procrestore(Proc *p)
+.PP
+.B
+int	procsaved(Proc *p)
+.PP
+.B
+void	procsave(Proc *p)
+.PP
+.B
+void	procwired(Proc *p, int machno)
+.PP
+.B
+void	scheddump(void)
+.PP
+.B
+void	schedinit(void)
+.PP
+.B
+char*	schedstats(char *s, char *e)
+.PP
+.B
+void	sched(void)
+.PP
+.B
+void	yield(void)
+.PP
+.EX
+Npriq        = 20,        /* scheduler priority levels */
+PriNormal    = 10,        /* base for normal processes */
+PriKproc     = 13,        /* base for kernel processes */
+PriRoot      = 13,        /* base for root processes */
+.EE
+.SH DESCRIPTION
+These functions define the priority process scheduler's interface.
+Processes are scheduled strictly by priority, and processor affinity.
+When possible, processes with no affinity will be rescheduled on
+the same processor.
+Within a priority, scheduling is round-robin.
+Long-running processes of the same priority are preempted and
+rescheduled.  But cpu use (or lack thereof) may adjust the priority
+up or down, unless it has been explicitly fixed.  Kernel processes
+are started with
+.B PriKproc
+while user processes start with
+.BR PriNormal .
+.PP
+.I Anyhigher
+returns true if any higher priority processes are runnable, while
+.I anyready
+returns true if any processes are runnable at all.
+.I Yield
+gives up the processor and pretends to consume ½ clock tick,
+while
+.I sched
+invokes the scheduler, potentially recursively.
+.I Sched
+may be called outside process context.  Either may return
+immediately.
+.I Schedinit
+initializes scheduling on the running processor.
+.PP
+.I Procpriority
+sets a process' priority directly.  Fixed-priority processes are not
+reprioritized based on cpu use.
+.I Procwired
+makes a process runnable only on a single processor.
+.PP
+.I Hzsched
+is called by the clock routine on every tick to collect statistics.
+Periodically
+ (typically once a second)
+.I hzsched
+reprioritizes based on cpu use.
+.PP
+.I Procsave
+and
+.I procrestore
+are architecture-dependent routines used by the scheduler to save
+and restore processes.
+.I Procsaved
+reliably determines if a process is not being run.
+.I Scheddump
+and
+.I schedstats
+print or return scheduler statistics.
+.SH SOURCE
+.B /sys/src/9/port/proc.c
+.SH DIAGNOSTICS
+.SH SEE ALSO
+.IR edf (9),
+.IR sleep (9)