Re: [GIT PULL] kdbus for 4.1-rc1

Steven Rostedt
2015-04-15T17:20:49Z

On Wed, 15 Apr 2015 18:40:33 +0200
Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:

> On Wed, Apr 15, 2015 at 11:41:53AM -0400, Steven Rostedt wrote:
> >
> > And obviously there is a lack of trust. And once kdbus is in, we must use
> > it, or support our own distro where we just do not have the time.
>
> Just like cgroups, and ftrace :)

Exactly.

>
> > Personally, I'm fine with getting something in that will help userspace
> > tools work better. The issue I see, mostly from the side lines as I haven't
> > totally submerged myself into the dbus protocol (I think I should spend
> > some time to do just that), this is going too fast. Once it is in the kernel,
> > whatever ABI we expose is locked in stone. There's no changing it. We need
> > to make sure that this is well thought out. People seem to be of the impression
> > that the current dbus design has flaws, but because everything relies on it
> > we must still push it into the kernel because it mimics what is out there
> > in user space. I disagree.
>
> "fast"? Are you kidding me? This stuff has been under active, public,
> development for over two years. We have been posting public patches,
> asking for review and comments for _months_ now. Given that there were
> no more specific review comments on the patch set, and its success in
> linux-next for almost the entire 4.0 development cycle, I asked it to be
> merged.
>
> I don't know too many other kernel features/drivers that have taken this
> long, or done this "slowly", do you?

What other features/drivers that you know introduce a major new IPC
user space interface that will be a core component of the system?

>
> > As others have said. We do not need to follow the dbus design. If we can supply
> > a better transport layer than what the kernel supplies today, then tools will
> > eventually merge to it away from dbus. Perhaps the kernel can supply just enough
> > to have dbus improve its speed, but not with the entire complex solution that
> > kdbus is presenting today.
>
> I originally thought this would work too. 8 months of work later, I was
> proven wrong, that will not work. Or it imposes too much additional
> work on userspace that really makes no sense at all. The in-kernel code
> isn't a lot (again, 13k lines, smaller than almost all of the drivers
> you are using today on an individual basis) It's also really fast, but
> with benchmarks, David and Andy have found some minor bottlenecks that
> can make things faster.
>
> Yes it seems complex, but read the documentation to get an idea of what
> is happening here. I think you will get a better appreciation of what
> is going on.

I read a bit of the documentation, but not enough. I really need to sit
down and play with code. That's the way I learn and understand.

-- Steve