Re: PREEMPT_RT benchmark

On Wed, Mar 10, 2021 at 05:07:47PM -0300, Michel Macena Oliveira wrote:

I'm currently developing a time benchmark application where I want
to measure a real time thread latency. My application is based on
Cyclictest from
the rt-tests suit.

...

I programmed in such way that it would be equivalent to Cyclict test

...

At least that's what I expected, but my latencies are much bigger than
Cyclictest ones.

I don't know the nature of the "time benchmark" application you are
writing.

Just a small hint that if you're doing any heavy OpenGL graphics within
that application, the latency can shoot up significantly. On some of our
Intel boxes, this can lead to an increase of 100-200 microseconds.

That's because since Intel Gen9+ GPUs, Intel shares the Last-Level Cache
(and thus also memory bandwidth) between the GPU and the CPU. This
benefits graphical applications, but hurts predicatbility significantly.

Good luck,

--
Ahmed S. Darwish
Linutronix GmbH