linux-kernel - Re: Dynamic configure max

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Message-Id: <200907310956.53816.lkml@morethan.org>
Date:	Fri, 31 Jul 2009 09:56:33 -0500
From:	"Michael S. Zick" <lkml@...ethan.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Robert Hancock <hancockrwd@...il.com>,
	Corrado Zoccolo <czoccolo@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-acpi@...r.kernel.org,
	venkatesh.pallipadi@...el.com
Subject: Re: Dynamic configure max_cstate

On Fri July 31 2009, Andi Kleen wrote:
> Andreas Mohr <andi@...as.de> writes:
> 
> > Instead we should strive for a far-reaching _generic_ mechanism
> > which gathers average latencies of various I/O activities/devices
> > and then uses some formula to determine the maximum (not necessarily ACPI)
> > idle latency that we're willing to endure (e.g. average device I/O reply latency
> > divided by 10 or so).
> 
> The interrupt heuristics in the menu cpuidle governour are already
> attempting this, based on interrupt rates (or rather
> wakeup rates) which are supposed to roughly correspond with IO rates
> and scheduling events together.
> 
> Apparently that doesn't work in this case. The challenge would
> be to find out why and improve the menu algorithm to deal with it.
> I doubt a completely new mechanism is needed or makes sense.
> 
> > And in addition to this, we should also take into account (read: skip)
> > any idle states which kill busmaster DMA completely
> > (in case of busmaster DMA I/O activities, that is)
> 
> This is already done.
> 

Almost - the VIA C7-M needs a bit of kernel command line help - -
But should be easily fixable when I or one of the VIA support people GATI.
(Bus snoops are only fully supported in C0 and C1 but idle=halt takes care of that.)

Mike
> -Andi


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