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Message-ID: <20080528163318.GG30285@linux.vnet.ibm.com>
Date: Wed, 28 May 2008 22:03:18 +0530
From: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To: "Chris Friesen" <cfriesen@...tel.com>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu,
a.p.zijlstra@...llo.nl, pj@....com,
Balbir Singh <balbir@...ibm.com>,
aneesh.kumar@...ux.vnet.ibm.com, dhaval@...ux.vnet.ibm.com
Subject: Re: fair group scheduler not so fair?
On Tue, May 27, 2008 at 12:13:46PM -0600, Chris Friesen wrote:
>> Can you check if this makes a difference for you as well?
>
> Initially it looked promising. I put pid 2498 in group A, and pids 2499
> and 2500 in group B. 2498 got basically a full cpu, and the other two got
> 50% each.
>
> However, I then moved pid 2499 from group B to group A, and the system got
> stuck in the following behaviour:
>
> 2498 cfriesen 20 0 3800 392 336 R 99.7 0.0 3:00.22 cat
> 2500 cfriesen 20 0 3800 392 336 R 66.7 0.0 1:39.10 cat
> 2499 cfriesen 20 0 3800 392 336 R 33.0 0.0 1:24.31 cat
>
> I reproduced this a number of times.
Thanks for trying this combination. I discovered a task-leak in this loop
(__load_balance_iterator):
/* Skip over entities that are not tasks */
do {
se = list_entry(next, struct sched_entity, group_node);
next = next->next;
} while (next != &cfs_rq->tasks && !entity_is_task(se));
if (next == &cfs_rq->tasks)
return NULL;
We seem to be skipping the last element in the task list always. In your
case, the lone task in Group a/b is always skipped because of this.
The following hunk seems to fix this:
@@ -1386,9 +1386,6 @@ __load_balance_iterator(struct cfs_rq *c
next = next->next;
} while (next != &cfs_rq->tasks && !entity_is_task(se));
- if (next == &cfs_rq->tasks)
- return NULL;
-
cfs_rq->balance_iterator = next;
if (entity_is_task(se))
Updated patch (on top of 2.6.26-rc3 +
http://programming.kicks-ass.net/kernel-patches/sched-smp-group-fixes/)
below. Pls let me know how it fares!
---
include/linux/sched.h | 4 ++++
init/Kconfig | 2 +-
kernel/sched.c | 5 ++++-
kernel/sched_debug.c | 3 ++-
kernel/sched_fair.c | 3 ---
5 files changed, 11 insertions(+), 6 deletions(-)
Index: current/include/linux/sched.h
===================================================================
--- current.orig/include/linux/sched.h
+++ current/include/linux/sched.h
@@ -698,7 +698,11 @@ enum cpu_idle_type {
#define SCHED_LOAD_SHIFT 10
#define SCHED_LOAD_SCALE (1L << SCHED_LOAD_SHIFT)
+#ifdef CONFIG_FAIR_GROUP_SCHED
+#define SCHED_LOAD_SCALE_FUZZ 0
+#else
#define SCHED_LOAD_SCALE_FUZZ SCHED_LOAD_SCALE
+#endif
#ifdef CONFIG_SMP
#define SD_LOAD_BALANCE 1 /* Do load balancing on this domain. */
Index: current/init/Kconfig
===================================================================
--- current.orig/init/Kconfig
+++ current/init/Kconfig
@@ -349,7 +349,7 @@ config RT_GROUP_SCHED
See Documentation/sched-rt-group.txt for more information.
choice
- depends on GROUP_SCHED
+ depends on GROUP_SCHED && (FAIR_GROUP_SCHED || RT_GROUP_SCHED)
prompt "Basis for grouping tasks"
default USER_SCHED
Index: current/kernel/sched.c
===================================================================
--- current.orig/kernel/sched.c
+++ current/kernel/sched.c
@@ -1534,6 +1534,9 @@ tg_shares_up(struct task_group *tg, int
unsigned long shares = 0;
int i;
+ if (!tg->parent)
+ return;
+
for_each_cpu_mask(i, sd->span) {
rq_weight += tg->cfs_rq[i]->load.weight;
shares += tg->cfs_rq[i]->shares;
@@ -2919,7 +2922,7 @@ next:
* skip a task if it will be the highest priority task (i.e. smallest
* prio value) on its new queue regardless of its load weight
*/
- skip_for_load = (p->se.load.weight >> 1) > rem_load_move +
+ skip_for_load = (p->se.load.weight >> 1) >= rem_load_move +
SCHED_LOAD_SCALE_FUZZ;
if ((skip_for_load && p->prio >= *this_best_prio) ||
!can_migrate_task(p, busiest, this_cpu, sd, idle, &pinned)) {
Index: current/kernel/sched_debug.c
===================================================================
--- current.orig/kernel/sched_debug.c
+++ current/kernel/sched_debug.c
@@ -119,7 +119,7 @@ void print_cfs_rq(struct seq_file *m, in
struct sched_entity *last;
unsigned long flags;
-#if !defined(CONFIG_CGROUP_SCHED) || !defined(CONFIG_USER_SCHED)
+#ifndef CONFIG_CGROUP_SCHED
SEQ_printf(m, "\ncfs_rq[%d]:\n", cpu);
#else
char path[128] = "";
@@ -170,6 +170,7 @@ void print_cfs_rq(struct seq_file *m, in
#ifdef CONFIG_FAIR_GROUP_SCHED
#ifdef CONFIG_SMP
SEQ_printf(m, " .%-30s: %lu\n", "shares", cfs_rq->shares);
+ SEQ_printf(m, " .%-30s: %lu\n", "h_load", cfs_rq->h_load);
#endif
#endif
}
Index: current/kernel/sched_fair.c
===================================================================
--- current.orig/kernel/sched_fair.c
+++ current/kernel/sched_fair.c
@@ -1386,9 +1386,6 @@ __load_balance_iterator(struct cfs_rq *c
next = next->next;
} while (next != &cfs_rq->tasks && !entity_is_task(se));
- if (next == &cfs_rq->tasks)
- return NULL;
-
cfs_rq->balance_iterator = next;
if (entity_is_task(se))
--
Regards,
vatsa
--
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