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    Subjectscheduler interactivity: timeslice calculation seem wrong
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    currently, nicer tasks (nice value toward -20) get larger timeslices,
    and less nice tasks (nice value toward 19) get small timeslices.

    this is contrary to all process scheduling theory i've read, and also
    contrary to my intuition.

    maybe it was done this way for fairness reasons, but that's another
    story...

    high priority (interactive) tasks should get small timeslices for best
    interactive feeling, and low priority (cpu hog) tasks should get large
    timeslices for best efficiency, anyway they can be preempted by higher
    priority tasks if needed.

    also, i think dynamic priority should be used for timeslice calculation
    instead of static priority. the reason is, if a low priority task get a
    priority boost (to prevent starvation, for example) it should use the
    small timeslice corresponding to it's new priority level, instead of
    using it's original large timeslice that can ruin the interactive feel.

    something like this: (Sorry, not tested...)

    PS: i've attached a small program to calculate and print the timeslices
    length from code ripped from linux-2.6.0-test3



    --- sched-orig.c Sat Aug 09 00:39:34 2003
    +++ sched.c Mon Aug 18 10:52:22 2003
    @@ -126,8 +126,8 @@
    * 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) ((p)->prio < MAX_RT_PRIO ? MIN_TIMESLICE :
    (MAX_TIMESLICE - \
    + ((MAX_TIMESLICE - MIN_TIMESLICE) *
    (MAX_PRIO-1-(p)->prio)/(MAX_USER_PRIO - 1))))

    static inline unsigned int task_timeslice(task_t *p)
    {


    Best regards,

    Eric St-Laurent

    --- sched-orig.c Sat Aug 09 00:39:34 2003
    +++ sched.c Mon Aug 18 10:52:22 2003
    @@ -126,8 +126,8 @@
    * 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) ((p)->prio < MAX_RT_PRIO ? MIN_TIMESLICE : (MAX_TIMESLICE - \
    + ((MAX_TIMESLICE - MIN_TIMESLICE) * (MAX_PRIO-1-(p)->prio)/(MAX_USER_PRIO - 1))))

    static inline unsigned int task_timeslice(task_t *p)
    {#include <stdio.h>

    #define HZ 1000
    #define MIN_TIMESLICE ( 10 * HZ / 1000)
    #define MAX_TIMESLICE (200 * HZ / 1000)
    #define MAX_USER_RT_PRIO 100
    #define MAX_RT_PRIO MAX_USER_RT_PRIO
    #define MAX_PRIO (MAX_RT_PRIO + 40)
    #define NICE_TO_PRIO(nice) (MAX_RT_PRIO + (nice) + 20)
    #define USER_PRIO(p) ((p)-MAX_RT_PRIO)
    #define MAX_USER_PRIO (USER_PRIO(MAX_PRIO))

    #define BASE_TIMESLICE(p) (MIN_TIMESLICE + \
    ((MAX_TIMESLICE - MIN_TIMESLICE) * (MAX_PRIO-1-p)/(MAX_USER_PRIO - 1)))

    #define BASE_TIMESLICE2(p) (MAX_TIMESLICE - \
    ((MAX_TIMESLICE - MIN_TIMESLICE) * (MAX_PRIO-1-p)/(MAX_USER_PRIO - 1)))

    #define BASE_TIMESLICE3(p) (prio < MAX_RT_PRIO ? MIN_TIMESLICE : (MAX_TIMESLICE - \
    ((MAX_TIMESLICE - MIN_TIMESLICE) * (MAX_PRIO-1-p)/(MAX_USER_PRIO - 1))))

    int main(int argc, char *argv[])
    {
    // original timeslice calculation
    for (int nice = -20; nice <= 19; nice++)
    printf("nice: %d, timeslice: %d ms\n", nice, BASE_TIMESLICE(NICE_TO_PRIO(nice)) * 1000 / HZ);

    printf("\n");

    // reversed timeslice calculation
    for (int nice = -20; nice <= 19; nice++)
    printf("nice: %d, timeslice: %d ms\n", nice, BASE_TIMESLICE2(NICE_TO_PRIO(nice)) * 1000 / HZ);

    printf("\n");

    // dynamic priority based timeslice calculation
    for (int prio = 0; prio < MAX_PRIO; prio++)
    printf("prio: %d, timeslice: %d ms\n", prio, BASE_TIMESLICE3(prio) * 1000 / HZ);

    return 0;
    }
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      Last update: 2005-03-22 13:47    [W:0.894 / U:0.004 seconds]
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