Updating the system_configuration wiki page on wiki.linuxaudio.org

[autostatic]

https://wiki.linuxaudio.org/wiki/system_configuration has been updated but is not fully up to par yet. I've looked at @x42's recommendations and changed the following things:

• Took out most part of the Timers section.
• Moved the building your own kernel page to a separate page.
• All references to excruciatingly old kernels have been removed.
• Replaced references to realtimeconfigquickscan with references to its successor, rtcqs.

Not sure about the kernel section though, maybe the installation part can go away and maybe the focus should be shifted towards what can be done from user space. Maybe some info on tickless kernels? And I'd like to add a section on power management.

Maybe we could discuss omissions, plain errors, suggestions or improvements in this thread.

Jeremy

[sunrat]

Nice work Jeremy! I signed up to edit the wiki over a year ago with updating in mind but got overwhelmed trying to sort current recommendations from legacy, and effective tweaks from snake oil. I'm just a mere user who likes tinkering but don't know code or kernel intricacies.

I would like to find more info on tickless timers pursuant to x42's suggestion in that link. (Be aware that project the link is about seems to have fallen by the wayside and is uncompleted). The Liquorix kernel I have used for a few years is not tickless. Where does one even find a tickless kernel without compiling?
I did some testing with the help of xruncounter and found the best results with all the rtcqs recommendations satisfied and this kernel line for my Intel i5-6500:

Code: Select all

GRUB_CMDLINE_LINUX_DEFAULT="quiet intel_idle.max_cstate=0 processor.max_cstate=1 threadirqs"

[autostatic]

Hi sunrat, thanks!

I would like to find more info on tickless timers pursuant to x42's suggestion in that link. (Be aware that project the link is about seems to have fallen by the wayside and is uncompleted). The Liquorix kernel I have used for a few years is not tickless. Where does one even find a tickless kernel without compiling?

If your kernel has CONFIG_NO_HZ_IDLE=y then you're running a tickless kernel, see https://www.kernel.org/doc/Documentatio ... /NO_HZ.txt:

An idle CPU that is not receiving scheduling-clock interrupts is said to
be "dyntick-idle", "in dyntick-idle mode", "in nohz mode", or "running
tickless". The remainder of this document will use "dyntick-idle mode".

I did some testing with the help of xruncounter and found the best results with all the rtcqs recommendations satisfied and this kernel line for my Intel i5-6500:

Code: Select all

GRUB_CMDLINE_LINUX_DEFAULT="quiet intel_idle.max_cstate=0 processor.max_cstate=1 threadirqs"

I've looked at the *.max_cstate parameters too (and also the idle parameter) but since I mainly use Ardour I prefer using the /dev/cpu_dma_latency method Ardour offers. From what I've understood this is effectively the same as the kernel parameters you're using, see also https://www.kernel.org/doc/Documentatio ... erface.txt.

[sunrat]

Hi sunrat, thanks!

I would like to find more info on tickless timers pursuant to x42's suggestion in that link. (Be aware that project the link is about seems to have fallen by the wayside and is uncompleted). The Liquorix kernel I have used for a few years is not tickless. Where does one even find a tickless kernel without compiling?

If your kernel has CONFIG_NO_HZ_IDLE=y then you're running a tickless kernel, see https://www.kernel.org/doc/Documentatio ... /NO_HZ.txt:

An idle CPU that is not receiving scheduling-clock interrupts is said to
be "dyntick-idle", "in dyntick-idle mode", "in nohz mode", or "running
tickless". The remainder of this document will use "dyntick-idle mode".

Now I'm more confused. Liquorix has CONFIG_NO_HZ_IDLE=y, but what does CONFIG_NO_HZ do? In the wiki is written

the CONFIG_NO_HZ means your kernel is tickless

Robin posted this:

x42
Jul '20

CONFIG_HZ_1000=y
CONFIG_HZ=1000

This is backwards, prefer a tickless kernel for reliable low latency and low jittter MIDI.

Liquorix has:

CONFIG_NO_HZ_COMMON=y
CONFIG_NO_HZ_IDLE=y
# CONFIG_NO_HZ_FULL is not set
# CONFIG_NO_HZ is not set
CONFIG_HZ_1000=y
CONFIG_HZ=1000

I would also like to see more about CPU governors. Maybe hardware frequency scaling in modern processors is better than the kernel software scaling. Again from x42:

On this i7, I don’t even need to change the CPU governor. CPU frequency change are orders or magnitude faster than audio process cycles.

Things I doubt effectiveness:
- Max user watches
- Swappiness

Things I want to know more about:
- Intel C-states and P-states

[autostatic]

Now I'm more confused. Liquorix has CONFIG_NO_HZ_IDLE=y, but what does CONFIG_NO_HZ do?

Nothing I think, it has been superseded by CONFIG_NO_HZ_IDLE.

In the wiki is written

the CONFIG_NO_HZ means your kernel is tickless

Thanks for spotting that, should be updated too.

]Liquorix has:

CONFIG_NO_HZ_COMMON=y
CONFIG_NO_HZ_IDLE=y
# CONFIG_NO_HZ_FULL is not set
# CONFIG_NO_HZ is not set
CONFIG_HZ_1000=y
CONFIG_HZ=1000

It has CONFIG_NO_HZ_IDLE=y so it's a tickless kernel.

I would also like to see more about CPU governors. Maybe hardware frequency scaling in modern processors is better than the kernel software scaling. Again from x42:

On this i7, I don’t even need to change the CPU governor. CPU frequency change are orders or magnitude faster than audio process cycles.

I'll look into that too!

Things I doubt effectiveness:
- Max user watches

Already comes with extra context in the wiki, does that need any change? See https://wiki.linuxaudio.org/wiki/system ... sysctlconf

- Swappiness

Already comes with extra context too.

Things I want to know more about:
- Intel C-states and P-states

Same here, see if I can fathom https://www.kernel.org/doc/Documentatio ... erface.txt.

[sysrqer]

I wonder if some mention of pipewire might be helpful?

As there is a section for SSDs perhaps it might be helpful to add something about NVMe drives. Do they need the same adjustments as SSDs?

[autostatic]

Hello sysrqer, good point about Pipewire. Haven't tried it myself though so if anyone knows anything sensible to say about it within the context of the article, go ahead! The section about SSDs could use some scrutiny too and I'll look into NVMe.

[Audiojunkie]

https://wiki.linuxaudio.org/wiki/system_configuration has been updated but is not fully up to par yet. I've looked at @x42's recommendations and changed the following things:

• Took out most part of the Timers section.
• Moved the building your own kernel page to a separate page.
• All references to excruciatingly old kernels have been removed.
• Replaced references to realtimeconfigquickscan with references to its successor, rtcqs.

Not sure about the kernel section though, maybe the installation part can go away and maybe the focus should be shifted towards what can be done from user space. Maybe some info on tickless kernels? And I'd like to add a section on power management.

Maybe we could discuss omissions, plain errors, suggestions or improvements in this thread.

Jeremy

Thank you so much for working on this!!

[Audiojunkie]

As I understand it, Pipewire is quite cool! You can run PulseAudio, JACK, ALSA, and Gstreamer tools on top of it. There is no need to actually mess with pipewire streams themselves (unless you need or want to). On top of Pipewire, all you need are a compatible JACK patch bay (like qpwgraph), the New Session Manager, a grapical front end (like Agordejo), and your JACK apps.

They have their own performance tuning suggestions, which closely mirror what is in the Wiki:

https://gitlab.freedesktop.org/pipewire ... nce-tuning


I'm still trying to wrap my head around all of it, but it looks like its going to make things not only better, but easier.