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

Vegard Nossum
2008-05-14T06:00:24Z

On Tue, May 13, 2008 at 11:19 PM, Andi Kleen <andi@firstfloor.org> wrote:
>
> > 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]

No, sorry, no power meter :-/

> > 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.

Yes, sorry, you are correct. I tested the idle=mwait only on the
desktop machine (P4, msr = 0), and it improved the IPI problem. (I
even rechecked right now, and it really does.)

Now I tested it on the laptop as well, and here it makes no difference.

Vegard

--
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
-- E. W. Dijkstra, EWD1036