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Old 07-13-2007, 01:06 PM   #1
draeath
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Registered: Jul 2007
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Post linux 2.6.21: Timer Frequency / Preempt


I'm building a 2.6.21 kernel for a 2-core 64-bit-capable i386 system. Specifics are: Pentium D 805, with 1gb of RAM. No ISA or PCI-Express. Sata present but unused. I will be running this as a desktop and it will be doing a variety of things: number crunching, compiling, media creation, media playback, gaming, etc.

What should I pick for a timer frequency? the help only mentions 250mhz and 300mhz, makes no mention of the slower setting and the 1ghz setting.

I would also like to know if I should choose voluntary-preempt or fully-preemtable.

These are all settings that are new to me, as the last kernel I built was 2.4 and the built-in help doesn't really tell why one would use the other settings, only in very specific cases to they outright say "you want that if you do this"

Is there a better place to find answers to this kind of thing?
 
Old 07-13-2007, 03:42 PM   #2
Mara
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Do you mean that option where you have 100Hz, 1000Hz, 250Hz and so on? Note that it's Hz, not MHz. The parameter specifies how often the timer interrupt runs. The higher the number, the more responsive the system potentially is. It uses more time every second in the timer routine, so higher number means (small) performance degradation. Note that, if I remember correctly, previous kernel versions used 100Hz and that was fine. Higher value is for real-time tasks and high responsibility. Normal user will rather not notice it.

You can also safely choose voluntary-preempt. The difference is in the number of places when switching can take place. When the kernel is not fully preemtable, certain passages may still use the processor when there's someone with better reason for it. As in the previous example, most users will not usually notice. Full preemption is designed for real-time systems. It brings an extra level of complication in certain places. If you do not have a clear reason to use it, you probably do not need it.
 
  


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