Gentoo Archives: gentoo-user

From: Alan McKinnon <alan.mckinnon@×××××.com>
To: gentoo-user@l.g.o
Subject: Re: [gentoo-user] Mounting /dev/sdaX on boot does not work
Date: Wed, 30 Jan 2008 18:53:58
In Reply to: Re: [gentoo-user] Mounting /dev/sdaX on boot does not work by Mateusz Mierzwinski
1 On Wednesday 30 January 2008, Mateusz Mierzwinski wrote:
2 > Alan McKinnon pisze:
4 > > One could try listing these drivers in /etc/autoload.d/kernel-2.6
5 > > but the easiest is probably to compile them into the kernel
6 >
7 > You have right. Standard unix kernel was designed to have all inside.
8 > I don't know why some people still prefer modules than monolith
9 > kernel. If you have modules, you must recompile all of them when new
10 > ABI comes out. On monolithic kernel its all there. Also i don't know
11 > if modules are not slower than monolith Kernel because of User space
12 > to Kernel space connection. Compiled in modules makes kernel run
13 > faster, and if it's server, then even 0.00001 sec makes the different
14 > on functions execution and internal core communication. Partly beyond
15 > of that problem is IPC module communication. But if there are
16 > benefits then also are problems with error code execution or beta
17 > drivers installed. Also if You have Molnar's Real Time Preemption
18 > Model on Your kernel, You should choose monolithic kernel. PS: some
19 > drivers are don't work as modules like they should. You see Windows -
20 > there are drivers like Linux modules - what it makes? Blue screens of
21 > death ;), but this is another story... ;)
23 That's an easy answer :-)
25 Standard Unix was designed for systems where you know exactly what
26 hardware you have up front and there are no nasty surprises. Take for
27 example an SGI box. How many PCI chipsets could it possibly have?
28 Exactly one. So you know exactly which driver you will need.
30 Apple are still lucky in this regard, as the only hardware that goes in
31 them is Apple's hardware and kernel configurationis then quite easy.
33 But we use the worst possible design that demented designers could ever
34 come up with - PCs. The range of stuff available is staggering. The
35 amount of dodgy hardware that claims to conform to spec but doesn't is
36 even more staggering. So now exactly which modules are you going to
37 compile in monolithically? What about hotpluggable hardware? As a
38 vendor you have no way of knowing which funky hardware the user will
39 ever plug into a notebook, and you simply cannot compile everything in
40 (never mind the driver conflicts you will have).
42 Gentoo expects their users to compile their own kernels so to a large
43 extent we can make stuff monolithic, apart from the hot-pluggable
44 devices.
46 Binary distros cannot do this. To conserve memory they must load only
47 the drivers for hardware that is actually present, and to do that one
48 needs modules. I don;t know of a binary commercial distro that will
49 gladly still support users who compile their own kernels - they usually
50 stuff it all up gloriously. It's a no-brainer really.
52 I don't buy the speedup argument either and have never seena benchmark
53 that proves modules are slower. The Linux kernel module loader is
54 essentially self-modifying code and inserts modules into kernel space
55 as if they had been there monolithically (within reason of course).
56 Some drivers do behave differently between being modular and
57 monolithic, but this is a function of a crappy coder and not a function
58 of modularity :-) If a piece of kernel code causes a BSOD, then it
59 will probably do it either way it is loadable as the code is probably
60 crappy.
62 A Real Time kernel is not suitable for a PC either - I can't think of
63 any RT application where a PC would be a *GOOD* choice. For that I
64 would be using the embedded arches with a board where as designer I
65 know exactly what is present and what isn't. Monolithic makes more
66 sense in that case. I can imagine why Ingo made that choice - with RT
67 he has to supply certain guarantees and probbaly can't do that with
68 modules coming and going all the time.
70 Basically. modern Linux is essentially unusable without kernel modules.
73 --
74 Alan McKinnon
75 alan dot mckinnon at gmail dot com
76 --
77 gentoo-user@l.g.o mailing list


Subject Author
Re: [gentoo-user] Mounting /dev/sdaX on boot does not work Mateusz Mierzwinski <mateuszmierzwinski@××.pl>