15 Jul
2010
15 Jul
'10
1:45 p.m.
On 07/15/2010 01:07 PM, Ralf Mardorf wrote:
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
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
> 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,
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? Cheers!
Ralf
best,
robin
--
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