linux-kernel - Re: [perfmon] Re: [perfmon2] perfmon2 merge news

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Message-ID: <20071114135104.GE6557@frankl.hpl.hp.com>
Date:	Wed, 14 Nov 2007 05:51:04 -0800
From:	Stephane Eranian <eranian@....hp.com>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	David Miller <davem@...emloft.net>, hch@...radead.org,
	akpm@...ux-foundation.org, gregkh@...e.de, mucci@...utk.edu,
	wcohen@...hat.com, robert.richter@....com,
	linux-kernel@...r.kernel.org, andi@...stfloor.org
Subject: Re: [perfmon] Re: [perfmon2] perfmon2 merge news


On Wed, Nov 14, 2007 at 10:44:56PM +1100, Paul Mackerras wrote:
> David Miller writes:
> 
> > This is my impression too, all of the things being done with
> > a slew of system calls would be better served by real special
> > files and appropriate fops.
> 
> Special files and fops really only work well if you can coerce the
> interface into one where data flows predominantly one way.  I don't
> think they work so well for something that is more like an RPC across
> the user/kernel barrier.  For that a system call is better.
> 
> For instance, if you have something that kind-of looks like
> 
> 	read_pmds(int n, int *pmd_numbers, u64 *pmd_values);
> 
> where the caller supplies an array of PMD numbers and the function
> returns their values (and you want that reading to be done atomically
> in some sense), how would you do that using special files and fops?
> 
Yes, the read call could be simplified to the level proposed above by Paul.

-- 
-Stephane
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