linux-kernel - Re: [PATCH 2/2] module: fix bne2 "gave up waiting for init of module libcrc32c"

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Date:	Wed, 2 Jun 2010 12:45:57 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Brandon Philips <brandon@...p.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>,
	Jon Masters <jonathan@...masters.org>,
	Tejun Heo <htejun@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [PATCH 2/2] module: fix bne2 "gave up waiting for init of module libcrc32c"

On Tue, 1 Jun 2010 02:49:50 pm Rusty Russell wrote:
> I wonder if we should just get rid of !CONFIG_UNLOAD then?  I have a soft spot
> for it because it keeps us honest and shows how much shit is there simply for
> our poor man's pagable kernel.
> 
> Let me compile up a kernel with and without and see what it's really doing
> to us...

With a distro-style config (copied Ubuntu then held down Enter on oldconfig)
it's:
		Vmlinux	module.o (text/data)	Total module size (text/data)
With unload	8976331	24144/1036		47255565/3298004
Without unload	8962022	20551/732		47176064/3222068
Without modules 8723931

So, we pay 14k for module unload support, or 0.2%, and 0.3% across the
modules themselves.  There's real runtime costs, too, but someone would need
to annotate and see how often we do inc/dec in a real system.

Not sure that last one is exactly comparable, but it looks like module
support is a significant cost...

Cheers,
Rusty.
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