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Too long latencies with latency test #124

Closed URSUroman closed 6 years ago

URSUroman commented 6 years ago

Basic Information:

RTXI Version:2afb5e58ff94be7bc3164ba26b203ee90c17b554 Installed from Live CD?:No, custom installation

Error Description:

I custom installed rtxi on an i7-7700K. When running the latency test (RT period like in http://rtxi.org/stats/ i.e. 10kHz), I get typically: RTH|----lat min|----lat avg|----lat max|-overrun|---msw|---lat best|--lat worst ... RTD| 0.710| 2.346| 121.659 | 3245| 0| 0.514| 1276.562 RTD| 0.675| 2.362| 131.398 | 3261| 0| 0.514| 1276.562 RTD| 0.704| 2.381| 356.757 | 3279| 0| 0.514| 1276.562 RTD| 0.551| 2.406| 687.567 | 3298| 0| 0.514| 1276.562 RTD| 0.673| 2.491| 1107.889| 3322| 0| 0.514| 1276.562 RTD| 0.703| 2.488| 1333.165| 3348| 0| 0.514| 1333.165 RTD| 0.558| 2.337| 130.778 | 3362| 0| 0.514| 1333.165 ...

lat max is always around 120 microsec. Sometimes, lat max is around 1200 microsec (this happens every 30-40 seconds).

If I understand it well, lat max should not exceed 20-30 microsecs.

When configuring the kernel, in menuconfig, I don't have the same options as at point 6 in http://rtxi.org/install/custom. This is probably because the doc was not yet adapted for the newer kernel. When trying to configure the kernel as consistent as possible with what is presented at point 6 of http://rtxi.org/install/, I realise that I can't disable the option: --> Power Management and ACPI options --> ACPI Support --> Processor (disable) unless I disable the whole ACPI support. Since there is a warning in menuconfig about ACPI being able to cause problems with xenomai, I disabled ACPI Support fully.

However, there is a second warning in menuconfig about CONFIG_MIGRATION. I can't get rid of it. I edited the .config file after menuconfig finished and before launching fakeroot make-kpkg \ --initrd \ --append-to-version=-xenomai-$xenomai_version \ --revision $(date +%Y%m%d) \ kernel-image kernel-headers modules I replaced "CONFIG_MIGRATION=y" with "#CONFIG_MIGRATION is not set" but after launching fakeroot make-kpkg ....., .config contains again "CONFIG_MIGRATION=y" as if something reset my change in .config.

Do you know what can cause max latencies of 120 microsec with bursts of 1200 microsecs? Is there a way to get rid of CONFIG_MIGRATION (in case it is the problem)? How can I edit .config so that the changes are taken over by the subsequent make-kpkg command ?

Best regards, Roman

URSUroman commented 6 years ago

Hello,

I think that the problem with too long latencies is due to the fact that I disabled the whole ACPI support. I must have disabled too much to ensure a proper functionning of the hardware. For example my processor's clock periodically increases its frequency and then decreases it....

I finally managed to disable only the options as presented in http://rtxi.org/install/custom To be able to disable the option --> Power Management and ACPI options --> ACPI Support --> Processor (disable)

I fist disabled all the other options that needed to be disabled (i.e. ponts 1, 2, 4 and then point 3).

Now the latencies of the system are similar to those expected: for a real-time frequency of 10kHz, the average latency is 2µs and maximal latencies are usually around 13 µs and exceptionalyl 20-30 µs.

Best regards, Roman

yapatel commented 6 years ago

Thank you for the excellent documentation and reporting of what you did to get it to work. This will be helpful for future users and we will include a reference to it in the documentation.