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By realtime I mean something that can help with fast network I/O; Low-latency and high-throughput.

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What would lead you to believe that there is an answer to this question that would be useful in any way? It is highly subjective, and almost certainly too localized. –  Zoredache Jun 7 '12 at 0:16
    
Should have been edited to title, "Suggestions for obtaining a free realtime Linux distribution". –  ewwhite Jun 7 '12 at 1:03
    
@JohnPristine What is the application for the realtime OS in your case? –  ewwhite Jun 7 '12 at 2:43
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1 Answer

I'd say CentOS or Scientific Linux with a realtime kernel compiled from Red Hat MRG source RPMs or using the CERN pre-built binaries.

See: Compiling realtime kernel from RHEL 6 MRG sources on CentOS 6

and CentOS 5 - realtime patch

The caveat is that simply installing a realtime distro won't automagically make everything faster. These kernels and related tools give you more "knobs" to tweak and ways to measure performance. This can be done for free (I've done it), but you will have to invest the time into working with your application and environment. Using the option I outlined, you can at least start with the RHEL MRG Tuning Guide.

On the tuning side, there's a lot more to work with in this realm. E.g.

  • Familiarize yourself with Ethtool and its options.
  • Investigate how interrupts work. E.g. what really happens when a NIC generates an interrupt. What does setting /proc/irq/irq_number/smp_affinity really do?
  • Understand CPU/process binding and realtime/rtctl priorities.

Other options include the commercial Concurrent RedHawk Linux (RHEL-like) and SuSE Enterprise Realtime. But they are costly distributions.

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Do you actually have any data or anything to support your suggestion that CentOS/Scientific/Redhat Linux is the fastest? Or are you just suggesting it because you are familiar with it? –  Zoredache Jun 7 '12 at 0:17
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The OP asked for a free realtime distribution. There are other solutions that can be tweaked and tuned, but they're expensive. I suggested a free path that can provide high performance (with the right tuning steps for the environment). –  ewwhite Jun 7 '12 at 0:25
    
That's awesome information! Thank you! I am not an IT guy so not sure I would be able to configure all that. I do understand IRQ, affinity, non-blocking, priorities, core isolation, etc. I wonder if I can buy this service from someone, in other words, if i can pay someone to install and configure a realtime os. –  JohnPristine Jun 7 '12 at 2:42
    
Yep. There are people who can provide this service. See my profile. –  ewwhite Jun 7 '12 at 2:52
    
@ewwhite How do I find your email in your profile? –  JohnPristine Jun 7 '12 at 14:25
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