"sched: add vslice" causes horrible interactivity under load

From: Benjamin K. Stuhl
Date: Sun Jan 27 2008 - 17:08:33 EST

I recently upgraded from 2.6.23.x to 2.6.24 and found that whereas
with 2.6.23.x I could have multiple "make -j3" compilation runs going
in the background with no real problems (on a dual-core Core 2), with
2.6.24 I get multiple-second lags when trying to switch tasks in KDE.
I did a git bisect starting from 9b73e76f3cf63379dcf45fcd4f112f5812418d0a
in Linus's 2.6.25 tree in the hope that the recent scheduler merge might
have fixed the problem, but no such luck. Instead, git bisect points its
all-knowing finger at

commit 67e9fb2a39a1d454218d50383094940982be138f
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Date: Mon Oct 15 17:00:10 2007 +0200

sched: add vslice

add vslice: the load-dependent "virtual slice" a task should
run ideally, so that the observed latency stays within the
sched_latency window.

Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

A straight-forward git revert crashes at boot, so I don't have a patch to offer. :-/
(Please keep me CC'ed, since I'm not subscribed to LKML.)

Thanks for your help,
-- BKS

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