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    SubjectRe: [PATCH] sched: fix interactive ceiling code
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    On Fri, 2006-05-19 at 11:30 +1000, Con Kolivas wrote:
    > Ingo, Andrew, I think these are minor logic fixes and comments that correct
    > a patch that has already been pushed to 2.6.17- and I would like them short
    > circuited to mainline if everyone is comfortable with it.
    >
    > Ken, Mike can I ask you to put a signed off on this patch for your
    > contributions please?

    Done.

    (I hope nobody ever rolls a patch from 30 contributors;)

    > Martin can I please ask for this to be put on test.kernel.org as a last
    > minute sanity check? I know URLs are easier so here is the patch for 2.6.17-rc4:
    > http://ck.kolivas.org/patches/crap/sched-fix_interactive_ceiling.patch
    >
    > ---
    > The relationship between INTERACTIVE_SLEEP and the ceiling is not perfect
    > and not explicit enough. The sleep boost is not supposed to be any larger
    > than without this code and the comment is not clear enough about what exactly
    > it does, just the reason it does it. Fix it.
    >
    > There is a ceiling to the priority beyond which tasks that only ever sleep
    > for very long periods cannot surpass. Fix it.
    >
    > Prevent the on-runqueue bonus logic from defeating the idle sleep logic.
    >
    > Opportunity to micro-optimise.
    >
    > Signed-off-by: Con Kolivas <kernel@kolivas.org>

    Signed-off-by: Mike Galbraith <efault@gmx.de>

    >
    > ---
    > kernel/sched.c | 52 +++++++++++++++++++++++++++-------------------------
    > 1 files changed, 27 insertions(+), 25 deletions(-)
    >
    > Index: linux-2.6.17-rc4/kernel/sched.c
    > ===================================================================
    > --- linux-2.6.17-rc4.orig/kernel/sched.c 2006-05-19 11:25:01.000000000 +1000
    > +++ linux-2.6.17-rc4/kernel/sched.c 2006-05-19 11:25:14.000000000 +1000
    > @@ -731,33 +731,35 @@ static inline void __activate_idle_task(
    > static int recalc_task_prio(task_t *p, unsigned long long now)
    > {
    > /* Caller must always ensure 'now >= p->timestamp' */
    > - unsigned long long __sleep_time = now - p->timestamp;
    > - unsigned long sleep_time;
    > + unsigned long sleep_time = now - p->timestamp;
    >
    > if (batch_task(p))
    > sleep_time = 0;
    > - else {
    > - if (__sleep_time > NS_MAX_SLEEP_AVG)
    > - sleep_time = NS_MAX_SLEEP_AVG;
    > - else
    > - sleep_time = (unsigned long)__sleep_time;
    > - }
    >
    > if (likely(sleep_time > 0)) {
    > /*
    > - * User tasks that sleep a long time are categorised as
    > - * idle. They will only have their sleep_avg increased to a
    > - * level that makes them just interactive priority to stay
    > - * active yet prevent them suddenly becoming cpu hogs and
    > - * starving other processes.
    > + * This ceiling is set to the lowest priority that would allow
    > + * a task to be reinserted into the active array on timeslice
    > + * completion.
    > */
    > - if (p->mm && sleep_time > INTERACTIVE_SLEEP(p)) {
    > - unsigned long ceiling;
    > + unsigned long ceiling = INTERACTIVE_SLEEP(p);
    >
    > - ceiling = JIFFIES_TO_NS(MAX_SLEEP_AVG -
    > - DEF_TIMESLICE);
    > - if (p->sleep_avg < ceiling)
    > - p->sleep_avg = ceiling;
    > + if (p->mm && sleep_time > ceiling && p->sleep_avg < ceiling) {
    > + /*
    > + * Prevents user tasks from achieving best priority
    > + * with one single large enough sleep.
    > + */
    > + p->sleep_avg = ceiling;
    > + /*
    > + * Using INTERACTIVE_SLEEP() as a ceiling places a
    > + * nice(0) task 1ms sleep away from promotion, and
    > + * gives it 700ms to round-robin with no chance of
    > + * being demoted. This is more than generous, so
    > + * mark this sleep as non-interactive to prevent the
    > + * on-runqueue bonus logic from intervening should
    > + * this task not receive cpu immediately.
    > + */
    > + p->sleep_type = SLEEP_NONINTERACTIVE;
    > } else {
    > /*
    > * Tasks waking from uninterruptible sleep are
    > @@ -765,12 +767,12 @@ static int recalc_task_prio(task_t *p, u
    > * are likely to be waiting on I/O
    > */
    > if (p->sleep_type == SLEEP_NONINTERACTIVE && p->mm) {
    > - if (p->sleep_avg >= INTERACTIVE_SLEEP(p))
    > + if (p->sleep_avg >= ceiling)
    > sleep_time = 0;
    > else if (p->sleep_avg + sleep_time >=
    > - INTERACTIVE_SLEEP(p)) {
    > - p->sleep_avg = INTERACTIVE_SLEEP(p);
    > - sleep_time = 0;
    > + ceiling) {
    > + p->sleep_avg = ceiling;
    > + sleep_time = 0;
    > }
    > }
    >
    > @@ -784,9 +786,9 @@ static int recalc_task_prio(task_t *p, u
    > */
    > p->sleep_avg += sleep_time;
    >
    > - if (p->sleep_avg > NS_MAX_SLEEP_AVG)
    > - p->sleep_avg = NS_MAX_SLEEP_AVG;
    > }
    > + if (p->sleep_avg > NS_MAX_SLEEP_AVG)
    > + p->sleep_avg = NS_MAX_SLEEP_AVG;
    > }
    >
    > return effective_prio(p);

    -
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