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Message-ID: <20070827204116.GA12495@elte.hu>
Date: Mon, 27 Aug 2007 22:41:16 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Al Boldi <a1426z@...ab.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Mike Galbraith <efault@....de>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org
Subject: Re: CFS review
* Al Boldi <a1426z@...ab.com> wrote:
> > Could you try the patch below instead, does this make 3x glxgears
> > smooth again? (if yes, could you send me your Signed-off-by line as
> > well.)
>
> The task-startup stalling is still there for ~10sec.
>
> Can you see the problem on your machine?
nope (i have no framebuffer setup) - but i can see some chew-max
latencies that occur when new tasks are started up. I _think_ it's
probably the same problem as yours.
could you try the patch below (which is the combo patch of my current
queue), ontop of head 50c46637aa? This makes chew-max behave better
during task mass-startup here.
Ingo
----------------->
Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h
+++ linux/include/linux/sched.h
@@ -904,6 +904,7 @@ struct sched_entity {
u64 exec_start;
u64 sum_exec_runtime;
+ u64 prev_sum_exec_runtime;
u64 wait_start_fair;
u64 sleep_start_fair;
Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -1587,6 +1587,7 @@ static void __sched_fork(struct task_str
p->se.wait_start_fair = 0;
p->se.exec_start = 0;
p->se.sum_exec_runtime = 0;
+ p->se.prev_sum_exec_runtime = 0;
p->se.delta_exec = 0;
p->se.delta_fair_run = 0;
p->se.delta_fair_sleep = 0;
Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -82,12 +82,12 @@ enum {
};
unsigned int sysctl_sched_features __read_mostly =
- SCHED_FEAT_FAIR_SLEEPERS *1 |
+ SCHED_FEAT_FAIR_SLEEPERS *0 |
SCHED_FEAT_SLEEPER_AVG *0 |
SCHED_FEAT_SLEEPER_LOAD_AVG *1 |
SCHED_FEAT_PRECISE_CPU_LOAD *1 |
- SCHED_FEAT_START_DEBIT *1 |
- SCHED_FEAT_SKIP_INITIAL *0;
+ SCHED_FEAT_START_DEBIT *0 |
+ SCHED_FEAT_SKIP_INITIAL *1;
extern struct sched_class fair_sched_class;
@@ -225,39 +225,15 @@ static struct sched_entity *__pick_next_
* Calculate the preemption granularity needed to schedule every
* runnable task once per sysctl_sched_latency amount of time.
* (down to a sensible low limit on granularity)
- *
- * For example, if there are 2 tasks running and latency is 10 msecs,
- * we switch tasks every 5 msecs. If we have 3 tasks running, we have
- * to switch tasks every 3.33 msecs to get a 10 msecs observed latency
- * for each task. We do finer and finer scheduling up to until we
- * reach the minimum granularity value.
- *
- * To achieve this we use the following dynamic-granularity rule:
- *
- * gran = lat/nr - lat/nr/nr
- *
- * This comes out of the following equations:
- *
- * kA1 + gran = kB1
- * kB2 + gran = kA2
- * kA2 = kA1
- * kB2 = kB1 - d + d/nr
- * lat = d * nr
- *
- * Where 'k' is key, 'A' is task A (waiting), 'B' is task B (running),
- * '1' is start of time, '2' is end of time, 'd' is delay between
- * 1 and 2 (during which task B was running), 'nr' is number of tasks
- * running, 'lat' is the the period of each task. ('lat' is the
- * sched_latency that we aim for.)
*/
-static long
+static unsigned long
sched_granularity(struct cfs_rq *cfs_rq)
{
unsigned int gran = sysctl_sched_latency;
unsigned int nr = cfs_rq->nr_running;
if (nr > 1) {
- gran = gran/nr - gran/nr/nr;
+ gran = gran/nr;
gran = max(gran, sysctl_sched_min_granularity);
}
@@ -489,6 +465,9 @@ update_stats_wait_end(struct cfs_rq *cfs
{
unsigned long delta_fair;
+ if (unlikely(!se->wait_start_fair))
+ return;
+
delta_fair = (unsigned long)min((u64)(2*sysctl_sched_runtime_limit),
(u64)(cfs_rq->fair_clock - se->wait_start_fair));
@@ -668,7 +647,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
/*
* Preempt the current task with a newly woken task if needed:
*/
-static void
+static int
__check_preempt_curr_fair(struct cfs_rq *cfs_rq, struct sched_entity *se,
struct sched_entity *curr, unsigned long granularity)
{
@@ -679,8 +658,11 @@ __check_preempt_curr_fair(struct cfs_rq
* preempt the current task unless the best task has
* a larger than sched_granularity fairness advantage:
*/
- if (__delta > niced_granularity(curr, granularity))
+ if (__delta > niced_granularity(curr, granularity)) {
resched_task(rq_of(cfs_rq)->curr);
+ return 1;
+ }
+ return 0;
}
static inline void
@@ -725,6 +707,7 @@ static void put_prev_entity(struct cfs_r
static void entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
+ unsigned long gran, delta_exec;
struct sched_entity *next;
/*
@@ -741,8 +724,13 @@ static void entity_tick(struct cfs_rq *c
if (next == curr)
return;
- __check_preempt_curr_fair(cfs_rq, next, curr,
- sched_granularity(cfs_rq));
+ gran = sched_granularity(cfs_rq);
+ delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
+ if (delta_exec > gran)
+ gran = 0;
+
+ if (__check_preempt_curr_fair(cfs_rq, next, curr, gran))
+ curr->prev_sum_exec_runtime = curr->sum_exec_runtime;
}
/**************************************************
@@ -1080,29 +1068,27 @@ static void task_new_fair(struct rq *rq,
sched_info_queued(p);
+ update_curr(cfs_rq);
update_stats_enqueue(cfs_rq, se);
- /*
- * Child runs first: we let it run before the parent
- * until it reschedules once. We set up the key so that
- * it will preempt the parent:
- */
- p->se.fair_key = current->se.fair_key -
- niced_granularity(&rq->curr->se, sched_granularity(cfs_rq)) - 1;
+
/*
* The first wait is dominated by the child-runs-first logic,
* so do not credit it with that waiting time yet:
*/
if (sysctl_sched_features & SCHED_FEAT_SKIP_INITIAL)
- p->se.wait_start_fair = 0;
+ se->wait_start_fair = 0;
/*
* The statistical average of wait_runtime is about
* -granularity/2, so initialize the task with that:
*/
- if (sysctl_sched_features & SCHED_FEAT_START_DEBIT)
- p->se.wait_runtime = -(sched_granularity(cfs_rq) / 2);
+ if (sysctl_sched_features & SCHED_FEAT_START_DEBIT) {
+ se->wait_runtime = -(sched_granularity(cfs_rq)/2);
+ schedstat_add(cfs_rq, wait_runtime, se->wait_runtime);
+ }
__enqueue_entity(cfs_rq, se);
+ resched_task(current);
}
#ifdef CONFIG_FAIR_GROUP_SCHED
-
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