[LAT] [LAD] Patching linux

Robin Gareus robin at gareus.org
Sun Aug 24 08:52:31 EDT 2008

Hash: SHA1

Rui Nuno Capela wrote:
> Robin Gareus wrote:
>> Rui Nuno Capela wrote:
>>> Tim Goetze wrote:
>>>> [Tim Goetze]
>>>>> [victor]
>>>>>> I was told to revert to (not possible in my specific
>>>>>> case, but there you go), in this list. Or to join the tuner's list.
>>>>> http://www.kernel.org/pub/linux/kernel/projects/rt/patch-
>>>>> worked for me.  Applied cleanly and compiled well after turning off
>>>>> some RCU-related preemption options that caused compilation errors,
>>>>> but I was in no mood to find out the exact how and why.  So far, it
>>>>> has collected a few hours of solid uptime too, but I haven't done
>>>>> any latency measuring.
>>>> Update: on my laptop, the patched kernel boots into an
>>>> endless list of tracebacks on the console.  On the main box, USB
>>>> MIDI input is only read as soon as a key is pressed on the USB
>>>> keyboard (the one with the letters, not the MIDI one ...).  USB MIDI
>>>> out is broken, too.  So it's back to the old version.
>>> ah, it seems i'm not alone.
>> hehe , nice try. We won't let you go that easily ;)
>>> i'm currently recovering myself from schock after returning from
>>> vacation and while trying 2.6.26.x-rt for the rentrýe it all seemed
>>> to work fine except omg... midi timing is a wreck, specially wrt.alsa
>>> sequencer. event delivery is completely fubar. i mean, completely.
>>> true showstopper, whatever :(
>>> cacophony seems to be the right word to express what it is.
>>> however, didn't had the time to check whether NOHZ is at stake. i'm
>>> certainly going back to 2.6.25.x-rt where things are still sane and
>>> pleasant for a while.
>>> btw, having NOHZ=y (aka tickless kernel) has been the norm here,
>>> since its inception
>> CONFIG_NO_HZ=y - same norm here; with good results iff it works.
> just tested here with NO_HZ not set in my (old) pentium4
> desktop.
> it just confirmed that NO_HZ is not the culprit here. midi events are
> still being delivered *completely* out of time and the funny thing is it
> just gets somewhat better whenever you hit the pc-keyboard keys.
> however, it all gets back to badness once you stop pressing any key (eg.
> shift-key)
> another funny thing goes that on a core2 duo T7200 laptop (x86_64) the
> same kernel config it runs all fine (NO_HZ=y)

http://kerneltrap.org/Linux/Removing_the_Big_Kernel_Lock mentions  TTY
drivers being a problem, actually "a long and difficult task"..


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