Re: Horrendous Audio Stutter - current git
From: Mike Galbraith
Date: Fri May 02 2008 - 08:09:59 EST
On Fri, 2008-05-02 at 07:10 -0400, Parag Warudkar wrote:
> Mike - the GROUP_SCHED stuff is set to y in the Ubuntu kernel and I
> have no audio skips - may be a regression introduced after 2.6.24?
Hm. I've stumbled across a regression that may be related. Can you
please try the attached with group scheduling enabled in current git?
-Mike
commit 8f1bc385cfbab474db6c27b5af1e439614f3025c
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Date: Sat Apr 19 19:45:00 2008 +0200
sched: fair: weight calculations
In order to level the hierarchy, we need to calculate load based on the
root view. That is, each task's load is in the same unit.
A
/ \
B 1
/ \
2 3
To compute 1's load we do:
weight(1)
--------------
rq_weight(A)
To compute 2's load we do:
weight(2) weight(B)
------------ * -----------
rq_weight(B) rw_weight(A)
This yields load fractions in comparable units.
The consequence is that it changes virtual time. We used to have:
time_{i}
vtime_{i} = ------------
weight_{i}
vtime = \Sum vtime_{i} = time / rq_weight.
But with the new way of load calculation we get that vtime equals time.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Index: linux-2.6.26.git/kernel/sched.c
===================================================================
--- linux-2.6.26.git.orig/kernel/sched.c
+++ linux-2.6.26.git/kernel/sched.c
@@ -1429,9 +1429,6 @@ static void __resched_task(struct task_s
*/
#define SRR(x, y) (((x) + (1UL << ((y) - 1))) >> (y))
-/*
- * delta *= weight / lw
- */
static unsigned long
calc_delta_mine(unsigned long delta_exec, unsigned long weight,
struct load_weight *lw)
@@ -1454,6 +1451,12 @@ calc_delta_mine(unsigned long delta_exec
return (unsigned long)min(tmp, (u64)(unsigned long)LONG_MAX);
}
+static inline unsigned long
+calc_delta_fair(unsigned long delta_exec, struct load_weight *lw)
+{
+ return calc_delta_mine(delta_exec, NICE_0_LOAD, lw);
+}
+
static inline void update_load_add(struct load_weight *lw, unsigned long inc)
{
lw->weight += inc;
Index: linux-2.6.26.git/kernel/sched_fair.c
===================================================================
--- linux-2.6.26.git.orig/kernel/sched_fair.c
+++ linux-2.6.26.git/kernel/sched_fair.c
@@ -334,34 +334,6 @@ int sched_nr_latency_handler(struct ctl_
#endif
/*
- * delta *= w / rw
- */
-static inline unsigned long
-calc_delta_weight(unsigned long delta, struct sched_entity *se)
-{
- for_each_sched_entity(se) {
- delta = calc_delta_mine(delta,
- se->load.weight, &cfs_rq_of(se)->load);
- }
-
- return delta;
-}
-
-/*
- * delta *= rw / w
- */
-static inline unsigned long
-calc_delta_fair(unsigned long delta, struct sched_entity *se)
-{
- for_each_sched_entity(se) {
- delta = calc_delta_mine(delta,
- cfs_rq_of(se)->load.weight, &se->load);
- }
-
- return delta;
-}
-
-/*
* The idea is to set a period in which each task runs once.
*
* When there are too many tasks (sysctl_sched_nr_latency) we have to stretch
@@ -390,54 +362,47 @@ static u64 __sched_period(unsigned long
*/
static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
- return calc_delta_weight(__sched_period(cfs_rq->nr_running), se);
+ u64 slice = __sched_period(cfs_rq->nr_running);
+
+ for_each_sched_entity(se) {
+ cfs_rq = cfs_rq_of(se);
+
+ slice *= se->load.weight;
+ do_div(slice, cfs_rq->load.weight);
+ }
+
+
+ return slice;
}
/*
* We calculate the vruntime slice of a to be inserted task
*
- * vs = s*rw/w = p
+ * vs = s/w = p/rw
*/
static u64 sched_vslice_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
unsigned long nr_running = cfs_rq->nr_running;
+ unsigned long weight;
+ u64 vslice;
if (!se->on_rq)
nr_running++;
- return __sched_period(nr_running);
-}
-
-/*
- * The goal of calc_delta_asym() is to be asymmetrically around NICE_0_LOAD, in
- * that it favours >=0 over <0.
- *
- * -20 |
- * |
- * 0 --------+-------
- * .'
- * 19 .'
- *
- */
-static unsigned long
-calc_delta_asym(unsigned long delta, struct sched_entity *se)
-{
- struct load_weight lw = {
- .weight = NICE_0_LOAD,
- .inv_weight = 1UL << (WMULT_SHIFT-NICE_0_SHIFT)
- };
+ vslice = __sched_period(nr_running);
for_each_sched_entity(se) {
- struct load_weight *se_lw = &se->load;
+ cfs_rq = cfs_rq_of(se);
- if (se->load.weight < NICE_0_LOAD)
- se_lw = &lw;
+ weight = cfs_rq->load.weight;
+ if (!se->on_rq)
+ weight += se->load.weight;
- delta = calc_delta_mine(delta,
- cfs_rq_of(se)->load.weight, se_lw);
+ vslice *= NICE_0_LOAD;
+ do_div(vslice, weight);
}
- return delta;
+ return vslice;
}
/*
@@ -454,7 +419,11 @@ __update_curr(struct cfs_rq *cfs_rq, str
curr->sum_exec_runtime += delta_exec;
schedstat_add(cfs_rq, exec_clock, delta_exec);
- delta_exec_weighted = calc_delta_fair(delta_exec, curr);
+ delta_exec_weighted = delta_exec;
+ if (unlikely(curr->load.weight != NICE_0_LOAD)) {
+ delta_exec_weighted = calc_delta_fair(delta_exec_weighted,
+ &curr->load);
+ }
curr->vruntime += delta_exec_weighted;
}
@@ -663,7 +632,8 @@ place_entity(struct cfs_rq *cfs_rq, stru
/* sleeps upto a single latency don't count. */
if (sched_feat(NEW_FAIR_SLEEPERS)) {
if (sched_feat(NORMALIZED_SLEEPER))
- vruntime -= calc_delta_weight(sysctl_sched_latency, se);
+ vruntime -= calc_delta_fair(sysctl_sched_latency,
+ &cfs_rq->load);
else
vruntime -= sysctl_sched_latency;
}
@@ -1162,10 +1132,11 @@ static unsigned long wakeup_gran(struct
unsigned long gran = sysctl_sched_wakeup_granularity;
/*
- * More easily preempt - nice tasks, while not making it harder for
- * + nice tasks.
+ * More easily preempt - nice tasks, while not making
+ * it harder for + nice tasks.
*/
- gran = calc_delta_asym(sysctl_sched_wakeup_granularity, se);
+ if (unlikely(se->load.weight > NICE_0_LOAD))
+ gran = calc_delta_fair(gran, &se->load);
return gran;
}