Re: [BISECTED] Lots of "rescheduling IPIs" in powertop

Andi Kleen
2008-05-13T21:20:00Z

> The desktop is a P4:
>
> processor : 0
> vendor_id : GenuineIntel
> cpu family : 15
> model : 6
> model name : Intel(R) Pentium(R) 4 CPU 3.00GHz
> stepping : 5
> cpu MHz : 2992.624
> cache size : 2048 KB

> flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx
> lm constant_tsc pebs bts pni monitor ds_cpl est tm2 cid cx16 xtpr
> lahf_lm
> bogomips : 5990.81
> clflush size : 64
>
> (similar for processor 1)
>
> # msr
> 0

Ok the CPU reports it doesn't support any C states in MWAIT. If that is
correct then it would be correct to not use MWAIT idle and might
actually save more power to not use it.

I don't know if that's true or not. Do you have a power meter perhaps?
If yes can you measure if there's a difference between mwait=idle /
default on your box when it is idle?

[cc Arjan he might now if that CPU is supposed to support C1 in MWAIT]

>
> The laptop is a Pentium Dual-Core:
>
> processor : 0
> vendor_id : GenuineIntel
> cpu family : 6
> model : 15
> model name : Intel(R) Pentium(R) Dual CPU T2310 @ 1.46GHz
> stepping : 13
> cpu MHz : 800.000
> cache size : 1024 KB
...
> flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca
> cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm
> constant_tsc arch_perfmon pebs bts pni monitor ds_cpl est tm2 ssse3
> cx16 xtpr lahf_lm
> bogomips : 2930.23
> clflush size : 64
>
> (similar for processor 1)
>
> # ./msr
> 1110

CPU reports it supports C1/C2/C3. Are you sure there is a difference on
that box? The code should have kept using MWAIT because it checks C1.
Please double check.

-Andi