From: Ingo Molnar <mingo@elte.hu>
The main benefit is that with the default HZ=1000 nice +19 tasks now get 5
msecs of timeslices, so the ratio of CPU use is linear. (nice 0 task gets
20 times more CPU time than a nice 19 task. Prior this change the ratio
was 1:10)
another effect is that nice 0 tasks now get a round 100 msecs of timeslices
(as intended), instead of 102 msecs.
here's a table of old/new timeslice values, for HZ=1000 and 100:
HZ=1000 ( HZ=100 )
old new ( old new )
nice -20: 200 200 ( 200 200 )
nice -19: 195 195 ( 190 190 )
...
nice 0: 102 100 ( 100 100 )
nice 1: 97 95 ( 90 90 )
nice 2: 92 90 ( 90 90 )
...
nice 17: 19 15 ( 10 10 )
nice 18: 14 10 ( 10 10 )
nice 19: 10 5 ( 10 10 )
i've tested the patch on x86.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/kernel/sched.c | 14 +++++++-------
1 files changed, 7 insertions(+), 7 deletions(-)
diff -puN kernel/sched.c~sched-timeslice-fix kernel/sched.c
--- 25/kernel/sched.c~sched-timeslice-fix Wed Aug 4 15:50:41 2004
+++ 25-akpm/kernel/sched.c Wed Aug 4 15:50:41 2004
@@ -80,11 +80,11 @@
/*
* These are the 'tuning knobs' of the scheduler:
*
- * Minimum timeslice is 10 msecs, default timeslice is 100 msecs,
- * maximum timeslice is 200 msecs. Timeslices get refilled after
- * they expire.
+ * Minimum timeslice is 5 msecs (or 1 jiffy, whichever is larger),
+ * default timeslice is 100 msecs, maximum timeslice is 200 msecs.
+ * Timeslices get refilled after they expire.
*/
-#define MIN_TIMESLICE ( 10 * HZ / 1000)
+#define MIN_TIMESLICE max(5 * HZ / 1000, 1)
#define MAX_TIMESLICE (200 * HZ / 1000)
#define ON_RUNQUEUE_WEIGHT 30
#define CHILD_PENALTY 95
@@ -172,9 +172,9 @@
* task_timeslice() is the interface that is used by the scheduler.
*/
-#define BASE_TIMESLICE(p) (MIN_TIMESLICE + \
- ((MAX_TIMESLICE - MIN_TIMESLICE) * \
- (MAX_PRIO-1 - (p)->static_prio) / (MAX_USER_PRIO-1)))
+#define BASE_TIMESLICE(p) \
+ max(MAX_TIMESLICE * (MAX_PRIO - (p)->static_prio) / (MAX_USER_PRIO), \
+ MIN_TIMESLICE)
static unsigned int task_timeslice(task_t *p)
{
_