linux-kernel - Re: [Bug #10710] [BISECTED] Lots of "rescheduling IPIs" in powertop

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Date:	Sun, 18 May 2008 22:30:30 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Vegard Nossum <vegard.nossum@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [Bug #10710] [BISECTED] Lots of "rescheduling IPIs" in powertop

Thomas Gleixner wrote:

> stop these pointless ad hominem attacks!

Just my experience from past incidents sorry. I'm sure it never happened
to you.

>> [In case someone is interested it's CPUID 5 ECX bit 0 which enumerates
>> if the MWAIT enumeration is there. So the correct mwait_usable() that
>> would have avoided your problem would be something like (untested):
>>
>> return c->cpuid_level >= 5 &&
>>            ((cpuid_ecx(5) & 1) == 0 || (cpuid_edx(5) >> 4) & 0xf) > 0);
>> ]
> 
> I'm interested, but I'd be even more interested in some useful pointer
> to the magic bitnumbers in that check, but don't exert yourself in
> providing the information,

It's documented in the IA32 SDM vol2 as part of the CPUID description.
It's a reasonable expection that everyone hacking on cpuid code has that
at hand.

-Andi
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