DBus in the kernel?

[Lennart Poettering]

On Mon, 04.01.10 16:40, Havoc Pennington (havoc.pennington at gmail.com) wrote:

> 
> What is the rationale for the bus itself in the kernel? Seems like one
> big pain in the ass, and I can't guess the motivation...

Primarily three things:

1) Getting rid of the double context switch for each msg. Right now
for the usual synchronous remote system call you need at least 4
context switches. If we can get rid of the message dispatching in
userspace we can reduce that to 2. On x86 the context switches
might be cheap, but on other CPUs (ARM) they are not.

2) This could allow eventual implementation of zero-copy data
transfer, which is already available for the traditional socket
types. That could make dbus viable as a trasnport for substantial
data, e.g. PCM data or video frames.

3) This can fix priority-inversion problems, since two high-priority
processes would not have to wait for a non-high-prio dbus daemon to
dispatch things. (unless you make the whole daemon high-prio which is
dangerous too however). This is actually a real problem.

And then, besides that it makes a lot of things more light-weight,
since memory consumption and copying is reduced, hence less cache
pressure, fewer processes, fds, other resources...

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4