high resolution timer support? yay or nay?

[BrutalGoerge]

It seems I can do 100Hz kernel with high res timer, or 1000Hz without high res timer, or 1000hz and high res timer... and all get the same fps... not sure if there's any diff in server stability either... but i didn't really test it hard.

What's the difference? What's better, if any?

[Monk]

You need to force enable HPET in the BIOS, or add "hpet=force" to your grub.conf next to your kernel line.

[BehaartesEtwas]

the differences are only marginal if you are really using hrtimers (and you do if you get ~1000 fps with HZ=100 in the kernel), because the higher HZ only increase the interrupt load thus are a little (but only a little) disturbing the server.

hpet is technically not really necessary for hrtimers, as there are other clock sources that can be used for that (e.g. apci)

[Monk]

You can't get good precision without HPET. ACPI sucks because it doesn't count at a fixed rate, and HPET reads from a memory mapped location. Some chipsets make it slower than ACPI, though due to whatever reason. On my hardware HPET is faster to read than ACPI, from userland.

[BehaartesEtwas]

I don't see any difference if I switch between HPET and ACPI, so it seems to be good enough at least on some systems... (I tested on several with ICH7, ICH8 and ICH10 chipset, never saw any difference..)