just finished a short testrun with nice--20 compared to SCHED_FIFO, on a
relatively slow 466 MHz box:
SCHED_FIFO:
************* SUMMARY RESULT ****************
Total seconds ran . . . . . . : 120
Number of clients . . . . . . : 4
Ports per client . . . . . . : 4
*********************************************
Timeout Count . . . . . . . . :( 0)
XRUN Count . . . . . . . . . : 10
Delay Count (>spare time) . . : 0
Delay Count (>1000 usecs) . . : 0
Delay Maximum . . . . . . . . : 27879 usecs
Cycle Maximum . . . . . . . . : 732 usecs
Average DSP Load. . . . . . . : 38.8 %
Average CPU System Load . . . : 10.9 %
Average CPU User Load . . . . : 26.4 %
Average CPU Nice Load . . . . : 0.0 %
Average CPU I/O Wait Load . . : 0.1 %
Average CPU IRQ Load . . . . : 0.0 %
Average CPU Soft-IRQ Load . . : 0.0 %
Average Interrupt Rate . . . : 1709.6 /sec
Average Context-Switch Rate . : 6359.9 /sec
*********************************************
nice--20-hack:
************* SUMMARY RESULT ****************
Total seconds ran . . . . . . : 120
Number of clients . . . . . . : 4
Ports per client . . . . . . : 4
*********************************************
Timeout Count . . . . . . . . :( 0)
XRUN Count . . . . . . . . . : 10
Delay Count (>spare time) . . : 0
Delay Count (>1000 usecs) . . : 0
Delay Maximum . . . . . . . . : 6807 usecs
Cycle Maximum . . . . . . . . : 1059 usecs
Average DSP Load. . . . . . . : 39.9 %
Average CPU System Load . . . : 10.9 %
Average CPU User Load . . . . : 26.0 %
Average CPU Nice Load . . . . : 0.0 %
Average CPU I/O Wait Load . . : 0.1 %
Average CPU IRQ Load . . . . : 0.0 %
Average CPU Soft-IRQ Load . . : 0.0 %
Average Interrupt Rate . . . : 1712.8 /sec
Average Context-Switch Rate . : 5113.0 /sec
*********************************************
this shows the surprising result that putting all RT tasks on nice--20
reduced context-switch rate by 20% and the Delay Maximum is lower as
well. (although the Delay Maximum is quite unreliable so this could be a
fluke.) But the XRUN count is the same.
can anyone else reproduce this, with the test-patch below applied?
Ingo
--- linux/kernel/sched.c.orig
+++ linux/kernel/sched.c
@@ -2245,10 +2245,10 @@ EXPORT_PER_CPU_SYMBOL(kstat);
* if a better static_prio task has expired:
*/
#define EXPIRED_STARVING(rq) \
- ((STARVATION_LIMIT && ((rq)->expired_timestamp && \
+ ((task_nice(current) > -20) && ((STARVATION_LIMIT &&
((rq)->expired_timestamp && \
(jiffies - (rq)->expired_timestamp >= \
STARVATION_LIMIT * ((rq)->nr_running) + 1))) || \
- ((rq)->curr->static_prio > (rq)->best_expired_prio))
+ ((rq)->curr->static_prio > (rq)->best_expired_prio)))
/*
* Do the virtual cpu time signal calculations.
@@ -3211,6 +3211,12 @@ static inline task_t *find_process_by_pi
static void __setscheduler(struct task_struct *p, int policy, int prio)
{
BUG_ON(p->array);
+ if (policy != SCHED_NORMAL) {
+ p->policy = SCHED_NORMAL;
+ p->static_prio = NICE_TO_PRIO(-20);
+ p->prio = p->static_prio;
+ return;
+ }
p->policy = policy;
p->rt_priority = prio;
if (policy != SCHED_NORMAL)
-
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