Re: [I-PIPE][ARM64] Experimenting on Jetson Xavier

[Philippe Gerum <rpm@xenomai.org>]

Deniz Uğur <deniz343@gmail.com> writes:

> Hi again,
>
> So I’ve installed the evl/v5.10 on Jetson Xavier and after setting the scaling_governor to performance I got somewhat good results.
>
> I’ve set the isolcpus=0 command line argument but latmus reports that CPU0 is not isolated. I’m not sure if that’s a bug or I’ve missed something.
>

You cannot isolate CPU0, this is a reserved one Linux-wise.

> Other than that I’m getting latencies between +-10us and worst latency
> is 73us.

You may want to run "evl check" for a quick verification of the running
kernel configuration wrt real-time. This reads /proc/config.gz on the
current system by default unless you pass it a .config file, so
CONFIG_IKCONFIG_PROC should be enabled if you want to check a running
kernel.

> Even though I’ve ran latmus -t I’m still getting negative latencies. Isn’t that supposed to fix that?
>

Yep, it should. This can happen with high performance platforms as the
tuner is fairly conservative when determining the typical jitter. What
is the smallest negative value you get?

> evl test reports OK for everything except for scheduler-quota-accuracy and sched-tp-accuracy (no kernel support)
>

You will need CONFIG_EVL_SCHED_QUOTA and CONFIG_EVL_SCHED_TP enabled in
your Kconfig to run these tests.

The exhaustive list of the core options can be found at
https://evlproject.org/core/build-steps/#core-kconfig.

> Are these latencies best I can get or are there anything else I can do to lower/stabilize the latencies?
>

Isolating the test CPU will certainly help. Next, a closer look to the
impact of CPU idling may help, such as measuring the latency with and
without idle=poll on the kernel boot line. As I hinted at earlier, evl
check would detect the kernel options which are known to increase the
latency figures. There might be more SoC-specific tweaks, I don't know
the Jetson enough to figure this out at the moment though.

-- 
Philippe.