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Message-ID: <20070828144604.GA13875@elte.hu>
Date: Tue, 28 Aug 2007 16:46:04 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Mike Galbraith <efault@....de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [git pull request] scheduler updates
* Mike Galbraith <efault@....de> wrote:
> On Tue, 2007-08-28 at 13:32 +0200, Ingo Molnar wrote:
> > Linus, please pull the latest scheduler git tree from:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched.git
> >
> > no big changes - 5 small fixes and 1 small cleanup:
>
> FWIW, I spent a few hours testing these patches with various loads,
> and all was peachy here. No multimedia or interactivity aberrations
> noted.
great! Btw., there's another refinement Peter and me are working on (see
the patch below): to place new tasks into the existing 'scheduling flow'
in a more seemless way. In practice this should mean less firefox spikes
during a kbuild workload. If you have some time to try it, could you add
the patch below to your tree too, and see what happens during fork-happy
workloads? It does not seem to be overly urgent to apply at the moment,
but it is a nice touch i think.
Ingo
------------------------>
Subject: sched: place new tasks in the middle of the task pool
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Place new tasks in the middle of the wait_runtime average. This smoothes
out latency spikes caused by freshly started tasks, without being unfair
to those tasks. Basically new tasks start right into the 'flow' of
wait_runtime that exists in the system at that moment.
[ mingo@...e.hu: changed it to use cfs_rq->wait_runtime ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
kernel/sched.c | 1
kernel/sched_fair.c | 59 +++++++++++++++++++++++++++++-----------------------
2 files changed, 33 insertions(+), 27 deletions(-)
Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -858,7 +858,6 @@ static void dec_nr_running(struct task_s
static void set_load_weight(struct task_struct *p)
{
- task_rq(p)->cfs.wait_runtime -= p->se.wait_runtime;
p->se.wait_runtime = 0;
if (task_has_rt_policy(p)) {
Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -86,8 +86,8 @@ unsigned int sysctl_sched_features __rea
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;
@@ -194,6 +194,8 @@ __enqueue_entity(struct cfs_rq *cfs_rq,
update_load_add(&cfs_rq->load, se->load.weight);
cfs_rq->nr_running++;
se->on_rq = 1;
+
+ cfs_rq->wait_runtime += se->wait_runtime;
}
static inline void
@@ -205,6 +207,8 @@ __dequeue_entity(struct cfs_rq *cfs_rq,
update_load_sub(&cfs_rq->load, se->load.weight);
cfs_rq->nr_running--;
se->on_rq = 0;
+
+ cfs_rq->wait_runtime -= se->wait_runtime;
}
static inline struct rb_node *first_fair(struct cfs_rq *cfs_rq)
@@ -326,9 +330,9 @@ __add_wait_runtime(struct cfs_rq *cfs_rq
static void
add_wait_runtime(struct cfs_rq *cfs_rq, struct sched_entity *se, long delta)
{
- schedstat_add(cfs_rq, wait_runtime, -se->wait_runtime);
+ cfs_rq->wait_runtime -= se->wait_runtime;
__add_wait_runtime(cfs_rq, se, delta);
- schedstat_add(cfs_rq, wait_runtime, se->wait_runtime);
+ cfs_rq->wait_runtime += se->wait_runtime;
}
/*
@@ -574,7 +578,6 @@ static void __enqueue_sleeper(struct cfs
prev_runtime = se->wait_runtime;
__add_wait_runtime(cfs_rq, se, delta_fair);
- schedstat_add(cfs_rq, wait_runtime, se->wait_runtime);
delta_fair = se->wait_runtime - prev_runtime;
/*
@@ -662,7 +665,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
if (tsk->state & TASK_UNINTERRUPTIBLE)
se->block_start = rq_of(cfs_rq)->clock;
}
- cfs_rq->wait_runtime -= se->wait_runtime;
#endif
}
__dequeue_entity(cfs_rq, se);
@@ -671,7 +673,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
/*
* Preempt the current task with a newly woken task if needed:
*/
-static int
+static void
__check_preempt_curr_fair(struct cfs_rq *cfs_rq, struct sched_entity *se,
struct sched_entity *curr, unsigned long granularity)
{
@@ -684,9 +686,8 @@ __check_preempt_curr_fair(struct cfs_rq
*/
if (__delta > niced_granularity(curr, granularity)) {
resched_task(rq_of(cfs_rq)->curr);
- return 1;
+ curr->prev_sum_exec_runtime = curr->sum_exec_runtime;
}
- return 0;
}
static inline void
@@ -762,8 +763,7 @@ static void entity_tick(struct cfs_rq *c
if (delta_exec > ideal_runtime)
gran = 0;
- if (__check_preempt_curr_fair(cfs_rq, next, curr, gran))
- curr->prev_sum_exec_runtime = curr->sum_exec_runtime;
+ __check_preempt_curr_fair(cfs_rq, next, curr, gran);
}
/**************************************************
@@ -1087,6 +1087,8 @@ static void task_tick_fair(struct rq *rq
}
}
+#define swap(a,b) do { __typeof__(a) tmp = (a); (a) = (b); (b)=tmp; } while (0)
+
/*
* Share the fairness runtime between parent and child, thus the
* total amount of pressure for CPU stays equal - new tasks
@@ -1102,14 +1104,27 @@ static void task_new_fair(struct rq *rq,
sched_info_queued(p);
update_curr(cfs_rq);
- update_stats_enqueue(cfs_rq, se);
+ if ((long)cfs_rq->wait_runtime < 0)
+ se->wait_runtime = (long)cfs_rq->wait_runtime /
+ (long)cfs_rq->nr_running;
/*
- * 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:
+ * The statistical average of wait_runtime is about
+ * -granularity/2, so initialize the task with that:
*/
- se->fair_key = curr->fair_key -
- niced_granularity(curr, sched_granularity(cfs_rq)) - 1;
+ if (sysctl_sched_features & SCHED_FEAT_START_DEBIT) {
+ __add_wait_runtime(cfs_rq, se,
+ -niced_granularity(se, sched_granularity(cfs_rq))/2);
+ }
+
+ update_stats_enqueue(cfs_rq, se);
+
+ if (sysctl_sched_child_runs_first && (se->fair_key > curr->fair_key)) {
+ dequeue_entity(cfs_rq, curr, 0);
+ swap(se->wait_runtime, curr->wait_runtime);
+ update_stats_enqueue(cfs_rq, se);
+ enqueue_entity(cfs_rq, curr, 0);
+ }
+
/*
* The first wait is dominated by the child-runs-first logic,
* so do not credit it with that waiting time yet:
@@ -1117,16 +1132,8 @@ static void task_new_fair(struct rq *rq,
if (sysctl_sched_features & SCHED_FEAT_SKIP_INITIAL)
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) {
- se->wait_runtime = -(sched_granularity(cfs_rq) / 2);
- schedstat_add(cfs_rq, wait_runtime, se->wait_runtime);
- }
-
__enqueue_entity(cfs_rq, se);
+ __check_preempt_curr_fair(cfs_rq, __pick_next_entity(cfs_rq), curr, 0);
}
#ifdef CONFIG_FAIR_GROUP_SCHED
-
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