Re: Real Time Behaviour of Linux

[Mark Hounschell <dmarkh@xxxxxxxxxx>]

Tharindu Rukshan Bamunuarachchi wrote:
> Dear All,
> 
> In summary, Vanilla Linux kernel gives average 3-4ms response time.
> But, when CONFIG_PREEMPT is turned on response is improved
> dramatically. Less than 100us (microseconds). I love that value.
> 
> 
> I have tried Three Different Linux kernels.
> 
> 1. Vanilla 2.6.9x
> 2. Vanilla + CONFIG_PREEMPT Enabled
> 3. Vanilla + Preemptible Patch
> 
> For each case I got following latencies in worst and best situations.
> 
> 1. Vanilla ---------------------------      Best(2000us)       
> Worst(~20000us)
> 2. CONFIG_PREEMPT -------      Best(75us)        Worst(700us)
> 
> 
> Actually all of above test were carried out using in-house small test
> program.
> Test program has two components and Server wakes up when client send
> some data.
> We are measuring Round Trip Time from client to server.Above values
> are in us = microsecond.
> 
> Actually, change of HZ value makes kernel unstable. I saw there are
> kernel code segments which assumes HZ value is either 1000, 250 or
> 512?? . However increase of HZ made kernel more responsive.
> 
> I am going to use 1000 HZ and CONFIG_PREEMPT for while. In next few
> days I will try to carry out some more performance test with
> Preemptible Patch and RT Linux.
> 
> Let you know the results of This Great Kernel.
> 
> 
> Like to thank all of your help and kind response to my mails.
> 


For a good test of your system see.

ftp://ftp.compro.net/public/rt-exec/rt-exec-1.0.3.tar.bz2

Mark

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