linux-kernel - Re: [patch 00/13] devtmpfs patches

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Date:	Mon, 11 May 2009 09:41:51 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Greg KH <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fabio Comolli <fabio.comolli@...il.com>,
	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org
Subject: Re: [patch 00/13] devtmpfs patches

On Mon, 11 May 2009 18:28:20 +0200
Kay Sievers <kay.sievers@...y.org> wrote:
> 
> It isn't slow. It's just that bootstrapping/re-constructing something
> later can obviously never be faster than doing it when the device is
> created.

the performance gains from doing stuff in batches is obviously well
established; CPU caches cause that. Not saying that's a hot factor
here, the total only takes 0.01 second after all, but "obviously" isn't
true here.


> I don't know of any obvious fixes to udev, otherwise I would have
> implemented them.

there's not much to fix afaics. It'd be nice if it was the 0.06 seconds
that Eric gets, but 0.20 isn't all that bad either.

> > sh < /sys/initial-device-list
> 
> And you still need to cope with the races, and bring up the event
> listener before that. 

so ?

> This is less reliable and always slower than the
> kernel provided nodes, besides that your /sys/initial-device-list will
> be the same amount of code we need for the node creation right away,
> without any of the other benefits, and will require another
> special-case tool we don't use today.

it's not about the amount of code. It's about in how many useful ways
the code can be used!

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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