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	Sat, 22 Mar 2008 06:26:46 PDT
Date: Sat, 22 Mar 2008 06:26:46 -0700 (PDT)
From: Barney Cordoba <barney_cordoba@yahoo.com>
To: Poul-Henning Kamp <phk@phk.freebsd.dk>,
	Julian Elischer <julian@elischer.org>
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Cc: current@freebsd.org
Subject: Re: kvm_read() vs ioctl performance 
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--- Poul-Henning Kamp <phk@phk.freebsd.dk> wrote:

> In message <47E46682.4020403@elischer.org>, Julian
> Elischer writes:
> 
> >>> tried a shared memory page?
> >> 
> >> No, but I built a test and kvm_read is 70 times
> >> faster, in
> >> case anyone is interested.
> 
> The shared memory approach is much better than that,
> you should
> go that way.
> 
> Look at the adlink driver for an example.

I can't easily follow this driver, given the superior
comments :) 

I don't see this in the handbook. Is there a document
which describes  both kernel and userland
implementation?

My concern is this: stats may be updated in iterations
of 100K+ times per second, while stats are only
gathered once every few seconds. Even a tiny addition
to the kernel cpu cycles can make it a "cut off your
head to stop a nosebleed" scenario. I don't want to
lose cpu cycles for the sake of saving a fraction of a
ms every few minutes.

Barney


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