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Subject[tip:sched/core] sched: Disable NEW_FAIR_SLEEPERS for now
Commit-ID:  3f2aa307c4d26b4ed6509d0a79e8254c9e07e921
Gitweb: http://git.kernel.org/tip/3f2aa307c4d26b4ed6509d0a79e8254c9e07e921
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Thu, 10 Sep 2009 20:34:48 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 10 Sep 2009 20:34:48 +0200

sched: Disable NEW_FAIR_SLEEPERS for now

Nikos Chantziaras and Jens Axboe reported that turning off
NEW_FAIR_SLEEPERS improves desktop interactivity visibly.

Nikos described his experiences the following way:

" With this setting, I can do "nice -n 19 make -j20" and
still have a very smooth desktop and watch a movie at
the same time. Various other annoyances (like the
"logout/shutdown/restart" dialog of KDE not appearing
at all until the background fade-out effect has finished)
are also gone. So this seems to be the single most
important setting that vastly improves desktop behavior,
at least here. "

Jens described it the following way, referring to a 10-seconds
xmodmap scheduling delay he was trying to debug:

" Then I tried switching NO_NEW_FAIR_SLEEPERS on, and then
I get:

Performance counter stats for 'xmodmap .xmodmap-carl':

9.009137 task-clock-msecs # 0.447 CPUs
18 context-switches # 0.002 M/sec
1 CPU-migrations # 0.000 M/sec
315 page-faults # 0.035 M/sec

0.020167093 seconds time elapsed

Woot! "

So disable it for now. In perf trace output i can see weird
delta timestamps:

cc1-9943 [001] 2802.059479616: sched_stat_wait: task: as:9944 wait: 2801938766276 [ns]

That nsec field is not supposed to be that large. More digging
is needed - but lets turn it off while the real bug is found.

Reported-by: Nikos Chantziaras <realnc@arcor.de>
Tested-by: Nikos Chantziaras <realnc@arcor.de>
Reported-by: Jens Axboe <jens.axboe@oracle.com>
Tested-by: Jens Axboe <jens.axboe@oracle.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <4AA93D34.8040500@arcor.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
kernel/sched_features.h | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index 4569bfa..e2dc63a 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -1,4 +1,4 @@
-SCHED_FEAT(NEW_FAIR_SLEEPERS, 1)
+SCHED_FEAT(NEW_FAIR_SLEEPERS, 0)
SCHED_FEAT(NORMALIZED_SLEEPER, 0)
SCHED_FEAT(ADAPTIVE_GRAN, 1)
SCHED_FEAT(WAKEUP_PREEMPT, 1)

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