Messages in this thread Patch in this message | | | Date | Mon, 23 May 2005 09:11:03 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] kernel <linux-2.6.11.10> kernel/sched.c |
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* Chen Shang <shangcs@gmail.com> wrote:
> /*===== ISSUE ====*/ > My second version of patch has a defect. > > + if (unlikely(old_prio != next->prio)) { > + dequeue_task(next, array); --> ### dequeue should against > old_prio, NOT next->prio ### > + enqueue_task(next, array); > + }
indeed...
> unforunately, dequeue_task does not accept the third parameter to make > adjustment. Personally, I feel it's good to add extra function as my > first version of patch to combine dequeue and enqueue together. > Reasons as following: > 1) adding the third parameter to dequeue_task() would cause other > places' code change; > 2) for schedule functions, performance is the first consideration. > Notice both dequeue_task() and enqueue_task() are NOT inline. > Combining those two in one saves one function call overhead;
the real problem comes from recalc_task_prio() having a side-effect, which makes requeueing of tasks harder. The solution is to return the prio from recalc_task_prio() - see the tested patch below. Agreed?
Ingo
--
micro-optimize task requeueing in schedule() & clean up recalc_task_prio().
From: Chen Shang <shangcs@gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
--- linux/kernel/sched.c.orig +++ linux/kernel/sched.c @@ -675,7 +675,7 @@ static inline void __activate_idle_task( rq->nr_running++; } -static void recalc_task_prio(task_t *p, unsigned long long now) +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; @@ -734,7 +734,7 @@ static void recalc_task_prio(task_t *p, } } - p->prio = effective_prio(p); + return effective_prio(p); } /* @@ -757,7 +757,7 @@ static void activate_task(task_t *p, run } #endif - recalc_task_prio(p, now); + p->prio = recalc_task_prio(p, now); /* * This checks to make sure it's not an uninterruptible task @@ -2751,7 +2751,7 @@ asmlinkage void __sched schedule(void) struct list_head *queue; unsigned long long now; unsigned long run_time; - int cpu, idx; + int cpu, idx, new_prio; /* * Test if we are atomic. Since do_exit() needs to call into @@ -2873,9 +2873,14 @@ go_idle: delta = delta * (ON_RUNQUEUE_WEIGHT * 128 / 100) / 128; array = next->array; - dequeue_task(next, array); - recalc_task_prio(next, next->timestamp + delta); - enqueue_task(next, array); + new_prio = recalc_task_prio(next, next->timestamp + delta); + + if (unlikely(next->prio != new_prio)) { + dequeue_task(next, array); + next->prio = new_prio; + enqueue_task(next, array); + } else + requeue_task(next, array); } next->activated = 0; switch_tasks: - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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