On 2017-02-05 19:11:01 [+0200], Ran Shalit wrote:

Hello,

Hi,

We made some testing on out cpu, installed with 4.1.15-rt17 kernel,
and we observed significant difference in latency between posic to
non-posix cyclictest benchmark.

with non posix we reach max ~50usec
while with posix we reach max ~170usec

On checking the exaples in cyclic test wiki, it seems that the
difference should not be that big :
https://rt.wiki.kernel.org/index.php/Cyclictest

What is the reason for such difference in behaviour ?
Does it mean we better use non-posix timer in application ?

As written in the other thread (regarding posix-timer):
I tested today v4.9-RT and didn't notice such high spikes between
clock_nanosleep and the posix timer. You have the consider that the
wakeup happens from ktimersoftirq so you have one additional context
switch here.
I general the clock_nansleep interface should be preferred if possible
to avoid that ctx switch.

Sebastian