On 27/08/14 19:21, Ken Teh wrote:
> When I first worked with it, it ran the 1.3 kernel and it was really
> fast. A 6µsec latency.  It got progressively worse with 2x kernels.  But
> still much better than the 150µsec quoted earler.

Just to clarify.  150µsec max latency is the certification criteria from
Red Hat.  Many hardware vendors does it far better.  Some require more
tweaking than others.  But once you've done that on appropriate
hardware, you can often reach down to 10-25µs max latency, with a
std.dev around 1-2µs.  But it is highly hardware and configuration
sensitive, and the lower latency you want the harder it gets.

In addition, software tuning is also a crucial point.  It's needed to
ensure that the latency sensitive software runs with realtime scheduling
and its priority isn't too low, as well as the kernel threads it depends
on (like networking tx/rx threads) - But also not too high priorities,
otherwise it may block important kernel threads doing their job.  But
doing this correctly, you can get really good results.


-- 
kind regards,

David Sommerseth