linux-kernel - Re: [GIT PULL] kdbus for 4.1-rc1

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Date:	Wed, 15 Apr 2015 23:16:38 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tom Gundersen <teg@...m.no>,
	"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: [GIT PULL] kdbus for 4.1-rc1

On Wed, 15 Apr 2015 11:28:58 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, Apr 15, 2015 at 11:18 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > I've seen this claimed, but I have never seen any actual numbers. What
> > speeds up? By how much? is it actually measurable?
> 
> And just to clarify: by "what speeds up, and by how much", I do _not_
> mean "sending a dbus message speeds up by 10x and avoids context
> switches". I've seen _those_ numbers. But does it actually matter?

In the desktop case some of the desktop folks manage to get themselves to
the point they send so many messages that it does. That's rather a
reflection on people programming performance critical code armed with
tools that are too easy to use combined with the fact that messaging is
hard to understand and model latency-wise.

There is a better way to fix those.

For MPI and some of the 'we used to run on an RT nano-kernel' people then
kdbus as proposed won't help - but they do have problems where
(particularly on very slow processors) Linux is naturally enough not that
comparable with a minimally memory protecting rtos doing atomic swaps on
pointers in a shared memory.

Alan
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