linux-kernel - Re: [PATCH v4 00/14] Add kdbus implementation

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Date:	Tue, 17 Mar 2015 12:24:50 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tom Gundersen <teg@...m.no>, Jiri Kosina <jkosina@...e.cz>,
	Linux API <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>
Subject: Re: [PATCH v4 00/14] Add kdbus implementation

On Mon, Mar 9, 2015 at 6:09 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> kdbus is a kernel-level IPC implementation that aims for resemblance to
> the the protocol layer with the existing userspace D-Bus daemon while
> enabling some features that couldn't be implemented before in userspace.
>

[...]

What changed from last time?

The discussion from last time about performance seems to have stalled.
kdbus is supposed to be fast -- that seems to be a large part of the
point.  Can anyone comment on how fast it actually is.  I'm curious
about:

 - The time it takes to do the ioctl to send a message

 - The time it takes to receive a message (poll + whatever ioctls)

 - The time it takes to transfer a memfd (I don't care about how long
it takes to create or map a memfd -- that's exactly the same between
kdbus and any other memfds user, I imagine)

 - The time it takes to connect

I'm also interested in whether the current design is actually amenable
to good performance.  I'm told that it is, but ISTM there's a lot of
heavyweight stuff going on with each send operation that will be hard
to remove.

--Andy
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