linux-kernel - Re: CPA patchset

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Message-ID: <20080110100712.GO25945@bingen.suse.de>
Date:	Thu, 10 Jan 2008 11:07:12 +0100
From:	Andi Kleen <ak@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Venki Pallipadi <venkatesh.pallipadi@...el.com>,
	suresh.b.siddha@...el.com, Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: CPA patchset

On Thu, Jan 10, 2008 at 11:04:43AM +0100, Ingo Molnar wrote:
> 
> * Andi Kleen <ak@...e.de> wrote:
> 
> > >   WBINVD isnt particular fast (takes a few msecs), but why is that a 
> > >   problem? Drivers dont do high-frequency ioremap-ing. It's 
> > >   typically only done at driver/device startup and that's it.
> > 
> > Actually graphics drivers can do higher frequency allocation of WC 
> > memory (with PAT) support.
> 
> but that's not too smart: why dont they use WB plus cflush instead? 

Because they need to access it WC for performance.

> ioremap() will always be slow and we dont care about stupid uses of it.

Uninterruptible msec latencies are too slow even for slow path
initialization code imho.

-Andi
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