Bugzilla – Bug 150318
Powersave interferes with DMA on VIA C3 Nehemiah
Last modified: 2007-06-05 11:20:19 UTC
This is a known problem on VIA EPIA boards, and VIA provide a fix on their website. If the CPU is told to change clock frequency while a disk DMA is in operation, the DMA stalls with the hard disk light on for several seconds before the DMA times out. Meanwhile all processes requiring disk access are frozen. The system then recovers. There has been debate amongst kernel developers as to the quality of VIA's fix (in the longhaul module) as it appears to be a hack to get round once instance of a more generic hardware shortfall. See here for a fuller report/debate: http://forums.viaarena.com/messageview.aspx?catid=28&threadid=68568&enterthread=y The VIA fix is here: http://www.viaarena.com/Guide/via%20fc2&fc3&fc4&ml10&ml10.1&ml10.2%20c3%20powersaver%20appnote%20ver0.81a.gz
And is it accepted by upstream yet? That's the requirement for us to be able to accept something like this.
Nigel, the mainline kernel actually has longhaul support now. Did you verify whether it works?
10.0 includes longhaul and, no, it doesn't work properly, which is why I reported this bug. See: /usr/src/linux-2.6.13-15.8/arch/i386/kernel/cpu/cpufreq/longhaul.c The necessary change is not in 2.6.15, and the VIA patch is off an earlier version than this (though they provide the source for the full module). Who needs to be informed to get it into the main kernel?
Could you please check the latest kernel for SL10.1 (available from ftp://ftp.suse.com/pub/projects/kotd) and let us know if it works there? Thanks! Pavel, I'm assigning this to you
I got "Service unavailable" trying to access the patch. I do not have via system at hand. What about simply disabling longhaul.c in kernel config, blacklisting it in powersave or something like that?
Nigel, do you still have that patch? Could you attach it as a file?
I can remove it from the powersave startup script if it is considered broken. The user can still enable it if he wants to - but on his own risk. So if you find out it is broken in 10.1 - just tell me :-)
Created attachment 69196 [details] VIA's version of power save module
...and diff against recent mainline. No, this does not look too good. VIA should just work with DaveJ to fix this. For now... Stefan, please remove longhaul support from powersave script.
Created attachment 69318 [details] diff between via's version and mainline
(In reply to comment #10) > For now... Stefan, please remove longhaul support from powersave script. Done for 10.1
so this is fixed for 10.1, and for 10.0 the workaround is simply to put CPUFREQD_MODULE="off" into /etc/sysconfig/powersave/cpufreq.