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Subject[REGRESSION] High, likely incorrect process cpu usage counters with kvm and 2.6.2[67]
Running an idle Windows VM on Linux 2.6.26+ with kvm, one sees high 
values for the kvm process in top (30%-70% cpu), where one would
normally expect 0%-1%. Surprisingly, the per-cpu system counters show
almost 100% idle, leading me to believe this is an accounting error and
that the process does not actually consume this much cpu.

I bisected this to a scheduler change, namely

commit 3e51f33fcc7f55e6df25d15b55ed10c8b4da84cd
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Sat May 3 18:29:28 2008 +0200

sched: add optional support for CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

this replaces the rq->clock stuff (and possibly cpu_clock()).

- architectures that have an 'imperfect' hardware clock can set
CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

- the 'jiffie' window might be superfulous when we update tick_gtod
before the __update_sched_clock() call in sched_clock_tick()

- cpu_clock() might be implemented as:

sched_clock_cpu(smp_processor_id())

if the accuracy proves good enough - how far can TSC drift in a
single jiffie when considering the filtering and idle hooks?

[ mingo@elte.hu: various fixes and cleanups ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Which is a bit too complex for me to work out.

Further information:
- the kvm thread which has the incorrect counter is the one that
actually executes guest code
- this thread mostly sleeps in schedule(), as one would expect
- it is periodically woken up by a timer; perhaps the problem is that
the process is sampled using the same timer, so it always shows as
running (though I'd expect it to report 100% cpu in that case).

Any help will be appreciated (or provided).

--
error compiling committee.c: too many arguments to function



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