[Bug 30570] Re: CPU usage very high with no running tasks using it

[João Manuel Rodrigues]

*** This bug is a duplicate of bug 30557 ***

I confirm.  Bug is still there in 2.6.15-25-686 #1 SMP PREEMPT kernel.

On my laptop (Acer Aspire 1692WLMi, Pentium M740 1.73 GHz),
With   echo 1 > /sys/module/processor/parameters/max_cstate
top reports tipically:
Cpu(s):  4.3% us,  0.3% sy,  0.0% ni, 95.0% id,  0.0% wa,  0.0% hi,  0.3% si

With  echo 2 > /sys/module/processor/parameters/max_cstate
I get:
Cpu(s): 54.5% us,  9.1% sy,  0.0% ni, 36.4% id,  0.0% wa,  0.0% hi,  0.0% si

This does not seem to be simply a problem with mis-reporting the CPU
usage.  The system actually feels slower when max_cstate is >= 2:
launching a firefox window is noticeably slower; I can actually see the
jumps as the window outline grows on-screen.  In fact, that is what
prompted me to look for bugs in the first place.  I'll try to back this
up with some benchmark later.  Also, I'll try and check this on a Core
Duo processor.  Has anyone done that?

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CPU usage very high with no running tasks using it
https://launchpad.net/bugs/30570