Re: Regression on rt kernel while using POSIX timers

["Patel, Vedang" <vedang.patel@intel.com>]

On Fri, 2017-02-10 at 20:07 +0100, Sebastian Andrzej Siewior wrote:
> On 2017-02-08 18:41:25 [+0000], Patel, Vedang wrote:
> > 
> > Hi, 
> Hi,
> 
> > 
> > The results for the POSIX timers were not as I expected. The
> > latency
> > for real-time kernel (v4.9.4-rt2) was worse compared to the
> > mainline
> > kernel (v4.9.4). In almost all the cases, the latency is almost
> > doubled
> >  with the max value reaching about 10 times when performing the
> > tests
> > under load.
> Is it also the case if you boost the priority of ktimersoftd/X
> threads?
> For clock_nanosleep, the wake-ups happen directly from hard-timer
> interrupt. For the posix-timer we have to delay those to the
> ktimersoftd
> thread which runs usually RT prio 1.
> 
I am getting very similar results even if I change the priority of
ktimersoftd to 99. Are there any recent rt patches which might have
changed the behaviour of POSIX timers? 

Also, are POSIX timers really suited for "real-time" applications?I
believe a similar question was raised by Ran Shalit a few days back: 
http://www.spinics.net/lists/linux-rt-users/msg16249.html

Thanks,
Vedang
> > 
> > Thanks,
> > Vedang Patel
> > Software Engineer
> > Intel Corporation
> Sebastian