Re: About rtla osnoise and timerlat usage

[Daniel Bristot de Oliveira <bristot@kernel.org>]

On 2/23/23 09:12, Prasad Pandit wrote:
> Hello Daniel,
> 
> On Thu, 23 Feb 2023 at 00:41, Prasad Pandit <ppandit@redhat.com> wrote:
>>      # trace-cmd record -p nop -e all -M 0x7FE -m 32000 --poll ~test/rt-tests/oslat --cpu-list 1-10 --duration 1h -w memmove -m 4K -T20
>>      ....
>>       Maximum:    14 11 13 12 12 13 12 11 12 10 (us)
>>       Max-Min:    13 10 12 11 11 12 11 10 11 9 (us)
>>       Duration:    3599.986 3599.986 3599.987 3599.987 3599.986 3599.987 3599.986 3599.987 3599.986 3599.986 (sec)
>>
>> * Running oslat(1) with SCHED_OTHER priority via 'trace-cmd --poll' option, did not show the spike. Nonetheless, trace-cmd(1) logs show  <idle>, ktimers/ and kworker/ threads running on isolated CPUs.
>> * Now running rtla-osnoise(1) test with SCHED_OTHER:
>>       # rtla osnoise top -c 1-10 -d 6h -s 20 -T 20 -Po:0 -q -t
> 
> Please see:
>     -> https://0bin.net/paste/ShXHmdvu#D0XY-WxTKCzWTxgQ+lTFbx1nB2TP2w+T0Mp8PBXt9gu
> 
> * rtla-osnoise(1) running for 6 hours with SCHED_OTHER and SCHED_FIFO,
> both did not report any spike above 20us.

Good!

>   It's reporting occurrence of IRQs only, all other noise columns are
> zero(0). That's a little surprising!?

Regarding the IRQs only: That is a good sign! your isolation is good!

Regarding the numbers: -T 20 is saying to the tracer to account as noise only
noise >= 20 us. As you did not hit a single case as your -s20 did not stop the trace,
that is expected.

But I think that what you want is -T 1. That is, consider a noise anything that is > than 1 us.

This will show you the noise added by those IRQs.

Anyways, the isolation is good enough to have good numbers with SCHED_OTHER... without
risks of starvation.

> Thank you.
> ---
>    - Prasad
>