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Change the scheduler to actually respect the PUSER barrier. It's been

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wrong for many years that negative niceness would lower the priority
of a process below PUSER, and once below PUSER, there were conditionals
in the code that are required to test for whether a process was in
the kernel which would break.

The breakage could (and did) cause lock-ups, basically nothing else
but the least nice program being able to run in some conditions.  The
algorithm which adjusts the priority now subtracts PRIO_MIN to do
things properly, and the ESTCPULIM() algorithm was updated to use
PRIO_TOTAL (PRIO_MAX - PRIO_MIN) to calculate the estcpu.

NICE_WEIGHT is now 1 to accomodate the full range of priorities better
(a -20 process with full CPU time has the priority of a +0 process with
no CPU time).  There are now 20 queues (exactly; 80 priorities) for
use in user processes' scheduling, and PUSER has been lowered to 48
to accomplish this.

This means, to the user, that things will be scheduled more correctly
(noticeable), there is no lock-up anymore WRT a niced -20 process
never releasing the CPU time for other processes.  In this fair system,
tsleep()ed < PUSER processes now will get the proper higher priority
than priority >= PUSER user processes.

The detective work of this was done by me, along with part of the
solution.  Luoqi Chen has provided most of the solution, and really
helped me understand what was happening better, to boot :)

Submitted by:   luoqi
Concept reviewed by:    bde
This commit is contained in:
Brian Feldman 2000-04-30 18:33:43 +00:00
parent 85a23112fd
commit 226f14bc83
4 changed files with 9 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
sys/kern/kern_synch.c
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@ -916,7 +916,7 @@ resetpriority(p)
if (p->p_rtprio.type == RTP_PRIO_NORMAL) {
newpriority = PUSER + p->p_estcpu / INVERSE_ESTCPU_WEIGHT +
NICE_WEIGHT * p->p_nice;
NICE_WEIGHT * (p->p_nice - PRIO_MIN);
newpriority = min(newpriority, MAXPRI);
p->p_usrpri = newpriority;
}

2
sys/sys/param.h
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@ -111,7 +111,7 @@
#define PCONFIG 32
#define PLOCK 36
#define PPAUSE 40
#define PUSER 50
#define PUSER 48
#define MAXPRI 127 /* Priorities range from 0 through MAXPRI. */
#define PRIMASK 0x0ff

8
sys/sys/proc.h
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@ -404,12 +404,12 @@ extern int whichidqs; /* Bit mask summary of non-empty Q's. */
* INVERSE_ESTCPU_WEIGHT is only suitable for statclock() frequencies in
* the range 100-256 Hz (approximately).
*/
#define ESTCPULIM(e) \
min((e), INVERSE_ESTCPU_WEIGHT * (NICE_WEIGHT * PRIO_MAX - PPQ) + \
INVERSE_ESTCPU_WEIGHT - 1)
#define INVERSE_ESTCPU_WEIGHT 8 /* 1 / (priorities per estcpu level) */
#define NICE_WEIGHT 2 /* priorities per nice level */
#define NICE_WEIGHT 1 /* priorities per nice level */
#define PPQ (128 / NQS) /* priorities per queue */
#define ESTCPULIM(e) \
min((e), INVERSE_ESTCPU_WEIGHT * (NICE_WEIGHT * PRIO_TOTAL - PPQ) + \
INVERSE_ESTCPU_WEIGHT - 1)
extern u_long ps_arg_cache_limit;
extern int ps_argsopen;

3
sys/sys/resource.h
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@ -42,6 +42,9 @@
*/
#define PRIO_MIN -20
#define PRIO_MAX 20
#ifdef _KERNEL
#define PRIO_TOTAL (PRIO_MAX - PRIO_MIN)
#endif /* _KERNEL */
#define PRIO_PROCESS 0
#define PRIO_PGRP 1