Re: [LAD] Timers, hpet, hrtimer

2009/11/10 <hollunder@email-addr-hidden>

> On Mon, 9 Nov 2009 17:43:12 +0100
> <hollunder@email-addr-hidden> wrote:
>
> > On Mon, 9 Nov 2009 16:47:07 +0100
> > <hollunder@email-addr-hidden> wrote:
> >
> > > On Mon, 09 Nov 2009 16:40:41 +0100
> > > Ralf Mardorf <ralf.mardorf@email-addr-hidden-dsl.net> wrote:
> > >
> > > > Emanuel Rumpf wrote:
> > > > > Opening the hr-timer with rosegarden freezes my whole system
> > > > > here, what could cause that ?
> > > > >
> > > >
> > > > I guess Open Octave is based on Rosegarden. While Qtractor is fine
> > > > with HR timer on my system, Open Octave freezes my system too. I
> > > > only was able to push reset, resp. I didn't try magic keys.
> > >
> > > Hmmm, I only find system-timer in either application.
> > > I recently found a line in dmesg that hpet wasn't enabled and I
> > > could try the boot option hpet=force.
> > > After doing this I have a /dev/hpet entry but still, only system, no
> > > rt or hpet in either app.
> > >
> > > Also no freezes tough ;)
> >
> > Ralf helped me a bit further off-list.
> > It seems I needed to modprobe snd-hrtimer
> > Now oom pretty much freezes as well when I tell it to use that,
> > qtractor doesn't complain, at least not immediately, couldn't try
> > further yet.
> >
> > Kernel is 2.6.31.4-rt14
> >
> > 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?
>
> Sorry for replying to myself again, but I'm still not sure about this
> point:
>
> chgrp audio /dev/hpet
> ... will make hpet usable for the group audio. <--?
>
> HR Timer as sequencer source will use HPET.
>
> Since hrtimer uses hpet if available and apps use hrtimer, why would I
> need to allow some audio group to access hpet directly?
> More so, changing the group of /dev/hpet seems very strange to me.
>
> Can someone please clarify?
>
> Regards,
> Philipp
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>

The only way to clarify is boot once with rc.local doing that, then again
without.

It's a character device, not raw, so this may not be needed. But on the
other hand, it _is_ a device, and if there needs to be I/O, there needs to
be r/w access, there needs to be permission.

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Received on Tue Nov 10 08:15:01 2009