linux-kernel - Re: [RFC PATCH 3/3] idle: store the idle state index in the struct rq

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Message-ID: <52F0FEF5.1010908@linux.intel.com>
Date:	Tue, 04 Feb 2014 06:53:41 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Morten Rasmussen <morten.rasmussen@....com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Len Brown <len.brown@...el.com>,
	Preeti Murthy <preeti.lkml@...il.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [RFC PATCH 3/3] idle: store the idle state index in the struct
 rq

> Yeah, so we could put the parameters back by measuring it in
> user-space via a nice utility in tools/, and by matching it to
> relevant hardware signatures (CPU type and cache sizes), plus doing
> some defaults for when we don't have any signature... possibly based
> on a fuzzy search to find the 'closest' system in the table of
> constants.
>
> That would stabilize the boot-to-boot figures while still keeping most
> of the system specific-ness, in a maintainable fashion.
>
> The downside is that we'd have to continuously maintain a table of all
> this info, with new entries added when new CPUs are introduced on the
> market. That's an upside too, btw.

for bigger systems this will also depend on the chipset and even motherboard
since inter-CPU communication may go via a 3rd party chip and the speed of that
will depend on how far they are apart...

like a 32 socket machine it'll be very different from a 2 socket machine,
and from the 32 socket machine from another vendor


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