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

["Deniz Uğur" <deniz343@gmail.com>]

Hi,

> I don't know
> the Jetson enough to figure this out at the moment though.

That’s more than okay, the EVL on Jetson works exceptionally good at the moment.
Anything more would be the cherry on top of it :)

I will take a look at CPU idling and “evl check” to be sure that I’ve done everything 
that I could do to lower the latency figures.

> What
> is the smallest negative value you get?

I’m getting around -0.5us after isolating the CPU#1 before that I was seeing around -7us.

> On 22 Feb 2021, at 11:39, Philippe Gerum <rpm@xenomai.org> wrote:
> 
> 
> 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.