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Date: Fri, 28 Oct 2016 16:37:26 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: David Herrmann <dh.herrmann@gmail.com>
Cc: linux-kernel@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>,
        Jiri Kosina <jikos@kernel.org>, Greg KH <greg@kroah.com>,
        Hannes Reinecke <hare@suse.com>, Steven Rostedt <rostedt@goodmis.org>,
        Arnd Bergmann <arnd@arndb.de>, Tom Gundersen <teg@jklm.no>,
        Josh Triplett <josh@joshtriplett.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC v1 09/14] bus1: provide transaction context for multicasts
Message-ID: <20161028143726.GJ3175@twins.programming.kicks-ass.net>
References: <20161026191810.12275-1-dh.herrmann@gmail.com>
 <20161026191810.12275-10-dh.herrmann@gmail.com>
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On Wed, Oct 26, 2016 at 09:18:05PM +0200, David Herrmann wrote:
> From: Tom Gundersen <teg@jklm.no>
> 
> The transaction engine is an object that lives on the stack and is used
> to stage and commit multicasts properly. Unlike unicasts, a multicast
> cannot just be queued on each destination, but must be properly
> synchronized. This requires us to first stage each message on their
> respective destination, then sync and tick the clocks, and eventual
> commit all messages.
> 
> The transaction context implements this logic for both, unicasts and
> multicasts. It hides the timestamp handling and takes care to properly
> synchronize accesses to the peer queues.
> 
> Signed-off-by: Tom Gundersen <teg@jklm.no>
> Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
> ---
>  ipc/bus1/Makefile |   1 +
>  ipc/bus1/peer.c   |   2 +
>  ipc/bus1/peer.h   |   3 +
>  ipc/bus1/tx.c     | 360 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  ipc/bus1/tx.h     | 102 ++++++++++++++++

See, this is way more than 4 lines.

You don't need any of this for causality.