[LAD] Timers, hpet, hrtimer

hollunder at gmx.at hollunder at gmx.at
Tue Nov 10 09:47:53 UTC 2009

On Tue, 10 Nov 2009 10:03:34 +0100
Clemens Ladisch <clemens at ladisch.de> wrote:

> hollunder at gmx.at wrote:
> > <hollunder at gmx.at> wrote:
> > > It seems I needed to modprobe snd-hrtimer
> > > Now oom pretty much freezes as well when I tell it to use that,
> Does oom or the entire system freeze?

In my case the whole system got almost in-responsive, mouse movement
took place once in a second or so, I guess it totally hogged the CPU. I
managed to revert the setting and everything returned to normal.

> > > Haven't tried this yet since I'm not sure it makes sense:
> > > chgrp audio /dev/hpet
> > > 
> > > So even when hpet is available, hrtimer is the one to use?
> > 
> > chgrp audio /dev/hpet
> > ... will make hpet usable for the group audio.  <--?
> /dev/hpet is a userspace interface for application that want to
> directly access the HPET device.  No applications (except Jack) want
> to do that; they use the standard high-resolution timer functions
> which internally use the HPET (or the LAPIC timer), but this is done
> in the kernel and is independent of the /dev/hpet interface.
> Clemens

Ok, thanks.
It seems jack doesn't use it by default either, only when it's run with
the option '-c h'. Only then it says:
This system has no accessible HPET device (Permission denied)

I'm wondering if this is necessary for best possible midi timing or


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