Date: Tue, 4 Feb 2014 10:14:05 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Len Brown <len.brown@intel.com>, Preeti Murthy <preeti.lkml@gmail.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        LKML <linux-kernel@vger.kernel.org>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        Lists linaro-kernel <linaro-kernel@lists.linaro.org>
Subject: Re: [RFC PATCH 3/3] idle: store the idle state index in the struct rq
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* Peter Zijlstra <peterz@infradead.org> wrote:

> [...]
>
> The reason Ingo took it out was that these measured numbers would 
> slightly vary from boot to boot making it hard to compare 
> performance numbers across boots.
> 
> There's something to be said for either case I suppose.

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.

Thanks,

	Ingo
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