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 <[EMAIL PROTECTED]>
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?
[ [EMAIL PROTECTED]: various fixes and cleanups ]
Signed-off-by: Peter Zijlstra <[EMAIL PROTECTED]>
Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
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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