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Re: adding system calls to an object based system
From: |
Neal H. Walfield |
Subject: |
Re: adding system calls to an object based system |
Date: |
Wed, 25 Jan 2006 21:25:07 +0100 |
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Wanderlust/2.14.0 (Africa) SEMI/1.14.6 (Maruoka) FLIM/1.14.6 (Marutamachi) APEL/10.6 Emacs/21.4 (i386-pc-linux-gnu) MULE/5.0 (SAKAKI) |
At Wed, 25 Jan 2006 16:34:14 -0300,
Leonardo Pereira wrote:
> As I know, those interfaces already exists.
Gianluca's proposal is to expose these interfaces directly at the
syscall level. Currently, the mechanisms are available via the
appropriate device object.
> So, I didn't understoo your "we
> shouldn't add such interfaces to Mach". I do not understand why someone
> would like to use IPC if we have an alternative that is faster than IPC.
> This is not related to a good or bad IPC, but the use of good
> mechanisms.
The sole motivation should not be performance. One of the advantages
of an object-based system is that inter-object dependencies must be
made explicit. This makes object relationships clearer and in doing
so reduces, in my experience, the number of inter-object dependencies.
The net result is, hopefully, a decrease in complexity and an increase
in robustness.
To achieve this, I think a microkernel should strive to have a single
system call, namely, IPC. Everything else should be built as an
object on top of that to which users invoke a capability naming the
object. That an object happens to be implemented by the kernel is
irrelevant.
That the IPC implementation is slow is, I agree, a problem. This
problem should be fixed at the IPC level or shown that this cannot be
done in a general way. Fixing Mach IPC will prove difficult: it works
well when memory is near CPU speed. L4 and EROS have shown that this
result need not be a categorical rejection of IPC based systems:
different IPC models can be fast.
Thanks,
Neal
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