Hi Vincent and Ying,
On 01/02/2017 04:42 PM, Vincent Guittot wrote:
Hi Ying,
On 28 December 2016 at 09:17, Huang, Ying <ying.hu...@intel.com> wrote:
Vincent Guittot <vincent.guit...@linaro.org> writes:
Le Tuesday 13 Dec 2016 . 09:47:30 (+0800), Huang, Ying a .crit :
Hi, Vincent,
Vincent Guittot <vincent.guit...@linaro.org> writes:
[...]
---
kernel/sched/fair.c | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 090a9bb..8efa113 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3138,6 +3138,31 @@ static inline int propagate_entity_load_avg(struct
sched_entity *se)
return 1;
}
+/* Check if we need to update the load and the utilization of a group_entity */
+static inline bool skip_blocked_update(struct sched_entity *se)
+{
+ struct cfs_rq *gcfs_rq = group_cfs_rq(se);
+
+ /*
+ * If sched_entity still have not null load or utilization, we have to
+ * decay it.
+ */
+ if (se->avg.load_avg || se->avg.util_avg)
+ return false;
+
+ /*
+ * If there is a pending propagation, we have to update the load and
+ * the utilizaion of the sched_entity
+ */
+ if (gcfs_rq->propagate_avg)
+ return false;
+
+ /*
+ * Other wise, the load and the utilizaiton of the sched_entity is
+ * already null so it will be a waste of time to try to decay it
+ */
+ return true;
+}
#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force) {}
@@ -6858,6 +6883,7 @@ static void update_blocked_averages(int cpu)
{
struct rq *rq = cpu_rq(cpu);
struct cfs_rq *cfs_rq;
+ struct sched_entity *se;
unsigned long flags;
raw_spin_lock_irqsave(&rq->lock, flags);
@@ -6876,7 +6902,8 @@ static void update_blocked_averages(int cpu)
update_tg_load_avg(cfs_rq, 0);
/* Propagate pending load changes to the parent */
- if (cfs_rq->tg->se[cpu])
+ se = cfs_rq->tg->se[cpu];
+ if (se && !skip_blocked_update(se))
update_load_avg(cfs_rq->tg->se[cpu], 0);
}
raw_spin_unlock_irqrestore(&rq->lock, flags);
The test result is as follow,
=========================================================================================
compiler/cpufreq_governor/freq/kconfig/nr_task/rootfs/samples/tbox_group/test/testcase:
gcc-6/powersave/20/x86_64-rhel-7.2/100%/debian-x86_64-2016-08-31.cgz/6000ss/lkp-hsw-d01/cache/ftq
commit:
4e5160766fcc9f41bbd38bac11f92dce993644aa: first bad commit
09a43ace1f986b003c118fdf6ddf1fd685692d49: parent of first bad commit
0613870ea53a7a279d8d37f2a3ce40aafc155fc8: debug commit with above patch
4e5160766fcc9f41 09a43ace1f986b003c118fdf6d 0613870ea53a7a279d8d37f2a3
---------------- -------------------------- --------------------------
%stddev %change %stddev %change %stddev
\ | \ | \
61670 ±228% -96.5% 2148 ± 11% -94.7% 3281 ± 58%
ftq.noise.25%
3463 ± 10% -60.0% 1386 ± 19% -26.3% 2552 ± 58%
ftq.noise.50%
1116 ± 23% -72.6% 305.99 ± 30% -35.8% 716.15 ± 64%
ftq.noise.75%
3843815 ± 3% +3.1% 3963589 ± 1% -49.6% 1938221 ±100%
ftq.time.involuntary_context_switches
5.33 ± 30% +21.4% 6.46 ± 14% -71.7% 1.50 ±108%
time.system_time
It appears that the system_time and involuntary_context_switches reduced
much after applied the debug patch, which is good from noise point of
view. ftq.noise.50% reduced compared with the first bad commit, but
have not restored to that of the parent of the first bad commit.
Thanks for testing. I will try to improve it a bit but not sure that I
can reduce more.
Is this a desktop system where this regression comes from autogroups (1
level taskgroups) or a server system with systemd (2 level taskgroups)?
Since the PELT rewrite (v4.2) I have ~60 autogroups per cpu
(&rq->leaf_cfs_rq_list) on my Ubuntu desktop system permanently (Intel
i7-4750HQ) whereas in v4.1 there were 0 - 10.
$ for i in `seq 0 7`; do cat /proc/sched_debug | grep
"cfs_rq\[$i\]:/autogroup-" | wc -l; done
58
61
63
65
60
59
62
56
Couldn't we still remove these autogroups by if (!cfs_rq->nr_running &&
!se->avg.load_avg && !se->avg.util_avg) in update_blocked_averages()?
Vincent, like we discussed in September last year, the proper fix would
probably be a cfs-rq->nr_attached which IMHO is not doable w/o being an
atomic because of migrate_task_rq_fair()->remove_entity_load_avg() not
holding the rq lock.
