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

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Date:	Wed, 14 May 2008 08:00:06 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Andreas Herrmann" <andreas.herrmann3@....com>,
	"\"S.Çağlar Onur\"" <caglar@...dus.org.tr>,
	Valdis.Kletnieks@...edu, "Matt Mackall" <mpm@...enic.com>,
	linux-kernel@...r.kernel.org, arjan@...radead.org
Subject: Re: [BISECTED] Lots of "rescheduling IPIs" in powertop

On Tue, May 13, 2008 at 11:19 PM, Andi Kleen <andi@...stfloor.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
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