dbus & preempt-rt compatibility patch

[Kay Sievers]

On Mon, Mar 10, 2014 at 5:37 PM, Simon McVittie
<simon.mcvittie at collabora.co.uk> wrote:
> On 10/03/14 15:01, VITIELLO Fabien wrote:
>> Do you think AF_BUS could be able to support hard real time ?
>>
>> http://www.ohloh.net/p/af_bus
>
> I don't think AF_BUS is any more likely to support hard realtime than
> kdbus, and it's never going to be merged in upstream Linux (it was
> specifically rejected by the networking maintainers), which means it's
> probably never going to be merged in dbus either.
>
>> I’m also looking for real time behaviour in kdbus but it’s hard to have
>> information in this topic. Do you know how to have best answers
>> concerning real time with kdbus ?
>
> "Wait for it to reach a ready-for-review state", I suspect.

There is nothing specific planned or on the kdbus side regarding
realtime behavior. In general, it should be easier to invent and
implement something than it is with the pure userspace dbus-daemon,
but I don't think anybody looks into anything related to that at this
moment.

Kdbus copies data directly (in the kernel, using an ioctl) from the
sending process to the receiver's buffer, there is no other process or
scheduling involved. Kdbus can also de-queue messages based on their
provided message priority. Kdbus supports synchronous method calls
with the ioctl interface. In theory, it might be possible to extend
the in-kernel logic to apply priority inheritance model like it exists
for the kernel's rt-mutexes.

But as said, this will unlikely happen anytime soon, or maybe it will
never happen, nobody really knows at this time.

Kay