cx_lowest and CPU usage
avg at icyb.net.ua
Fri Feb 1 07:37:50 PST 2008
on 29/01/2008 19:31 Nate Lawson said the following:
> Andriy Gapon wrote:
>> Report for 7.0-RC1 on quite old hardware: 440BX-based motherboard,
>> 450Mhz Pentium III (Katmai).
>> cx_supported claims to support C1, C2, C3. If I set cx_lowest to C3 it
>> immediately gets backed out to C2 with a kernel message about too many
>> short sleeps. But that's not a problem.
>> There is a weird thing: if I change cx_lowest to C2 when the machine is
>> completely idle, top shows that CPU usage for interrupts immediately
>> jumps to almost 20%. Change cx_lowest to C1, CPU usage drops back to
>> almost 0%.
>> Is this normal ?
>> If not, does this indicate some problem in idle routine or is this just
>> incorrect statistics calculation ? Or maybe something with HW ?
> Leave it at C1. Apparently C2 and C3 don't work on your machine.
> That's understandable with older, non-laptop hw.
I understand the advice. I event see that the code has the following
comment "Disable C3 support for all PIIX4 chipsets", but apparently it
does a little bit different thing.
Out of curiosity, what could be wrong with C2 state ?
vmstat -i reports identical interrupt rates with both cx_lowest=C1 and
cx_lowest=C2, so I wonder where from the extra interrupt CPU utilization
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