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/dev/rtc not found???

Posted: Wed Nov 11, 2009 2:10 pm
by angelsguitar
Hi all.

I was checking the realtime performance on various distros i have on my machine and tweaking to get it better. So far, the best performing distro I have installed is 64 Studio 3 Beta (compared to AVLinux 2r2, sidux 2009-02 with rt kernel, and Ubuntu Studio 9.10). However, it amazes me to find out that, when I ran the realTimeConfigQuickScan.pl script on 64 Studio, it says that the system can't find /dev/rtc.

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angelsguitar@64studio:~$ ./realTimeConfigQuickScan.pl 
Checking if you are root... no - good.
Finding current kernel config... found /proc/config.gz.
Checking for Ingo Molnar's Real-Time Preemption... found - good.
Checking for high-resolution timers... found - good.
Checking for Generic PCI bus-master DMA support... not found.
** Kernel without Generic PCI bus-master DMA support
   For more information, see:
   - http://lowlatency.linuxaudio.org
Checking for 1000hz clock... found - good.
Checking for High Resolution Timers... found - good.
Checking filesystem types... ok.
Checking tmpfs mounted on /tmp..  not found.
** Warning: no tmpfs partition mounted on /tmp
   For more information, see:
   - http://wiki.linuxmusicians.com/doku.php?id=system_configuration#tmpfs
   - http://lowlatency.linuxaudio.org
Checking filesystem 'noatime' parameter... 
** Warning: /media/cdrom0 does not have the 'noatime' parameter set
   For more information, see http://wiki.linuxmusicians.com/doku.php?id=system_configuration#filesystems
Checking the ability to prioritize processes with (re)nice... yes - good.
Checking the ability to prioritize processes with rtprio... yes - good.
Checking whether you're in the 'audio' group... yes - good.
Checking for multiple 'audio' groups... no - good.
Checking access to the real-time clock... not found.
** Warning: /dev/rtc not found.
Checking sysctl settings:
- checking inotify max_user_watches... >= 524288 - good.
Checking for resource-intensive background processes... none found - good.
I know the saying: "if it ain't broken, don't fix it" (or something like that..) However, I'd like to understand the reason of this; maybe it can help me get better performance in other distros. Isn't that supposed to negatively affect performance? How is it possible that it performs great in this condition? Or is this some kind of erroneous report?

Re: /dev/rtc not found???

Posted: Wed Nov 11, 2009 2:25 pm
by thorgal
well, it's funny you mention this because there's a discussion thread on LAD about hpet, the high precision event timer, which replaces rtc.

Check that you have /dev/hpet instead.

The recent kernels try to use HPET instead of RTC, thanks to the HR-Timer code introduced in them a while ago. HPET is found on any modern mobo.

ALSA can use it for its sequencer via its module snd_hrtimer.

jack can use as well directly if you specify the clock source in its options:

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jackd -R -P 70 -ch ... blabla ...
The "-ch" means clocksource=hpet

Re: /dev/rtc not found???

Posted: Thu Nov 12, 2009 2:27 am
by angelsguitar
Well, you are right. It has a /dev/hpet . Thanks for the info.

In that case, it would be great to include this check in the script.

Re: /dev/rtc not found???

Posted: Tue May 11, 2010 10:20 am
by Alexdelight
Wow it's nice))) :lol: