linuxaudio.org

On 07/15/2010 01:07 PM, Ralf Mardorf wrote:

quoted text
> On Thu, 2010-07-15 at 12:55 +0200, Clemens Ladisch wrote:

>> Ralf Mardorf wrote:

>>> - instead of dev.hpet.max-user-freq=64 I'll try 1024 or 2048 as Robin

>>> mentioned

>>

>> This parameter will not have any effect on anything because there is no

>> program that uses the HPET timers from userspace. 

That'd be correct if Ralf would stick to 'amidiplay' and friends for his

tests.
There are a couple of audio-tools who can use either RTC or HPET for

timing, although most of them need an option to explicitly enable it.
>> When high-resolution

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>> timers are used by ALSA, this is done inside the kernel where there is

>> no limit on the maximum frequency.

Thanks for that explanation. It makes perfect sense.

I take it the same must be true for dev.rtc.max-user-freq as well.
BTW. Do you know the unit of these values?

  cat /sys/class/rtc/rtc0/max_user_freq

  cat /proc/sys/dev/hpet/max-user-freq

are they Hz?
linux-2.6/Documentation/hpet.txt does not mention it at all and

linux-2.6/Documentation/rtc.txt hints it's Hz but does not explicitly

say so.
>> Regards,

quoted text
>> Clemens

>

> IIRC someone on jack-devel mailing list had issues when using mplayer

> with the value 64 and it was solved when using the value 1024. But as I

> mentioned before, for my USB MIDI there was a difference between system

> timer and hr timer, but there was no difference for the value 64 and

> 1024, when using hr timer.

>

> Btw. I don't understand what a maximum frequency in the context does

> mean. If 64 or 1024 should have impact, what would be the result?

>

> System timer for a kernel-rt is set up to 1000Hz and hr timer is at

> 1000000000Hz.

>

> What is 'max-user-freq' for?

It limits the maximum frequency at which user-space applications can

[request to] receive "wakeup calls" from the hr-timer.
see also the "Timers" thread on LAD last November:

http://linuxaudio.org/mailarchive/lad/2009/11/7/161647
> Cheers!

quoted text
>

> Ralf

>

>

best,

robin

--

Robin Gareus                           mail: robin@gareus.org

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