Hi Grant,
Have you tried to compile the kernel with low-latency + preemtion option
which is supposed to allow userspace applications to react faster? I
believe that the default is 'server' mode. I
think 'Low-Latency Desktop' mode may give you better performance.
Here is what your linux config option will look like:
Processor type and features
Preemption Model
( ) No Forced Preemption (Server)
( ) Voluntary Kernel Preemption (Desktop)
(x) Preemptible Kernel (Low-Latency Desktop)
Let us know if your performance improves by trying any of these options,
Dave
Grant Edwards wrote:
> I've been doing some performance tests comparing eCos and
> uClinux on a NIOS2 platform. TCP throughput is comparable
> (uClinux does a bit better with only 1 connection&thread, and
> eCos does a bit better at 32 connections&threads). But, latency
> on uClinux is much worse. The table below shows the time in
> milliseconds required for a user-space thread on an otherwise
> idle system to receive a small message (two bytes) via TCP and
> echo it back (10 trials):
>
> eCos uClinux
> ------- -------
> 1.864 8.151
> 2.079 4.509
> 1.972 7.699
> 1.871 7.189
> 1.728 5.152
> 1.842 6.803
> 1.733 7.041
> 1.847 3.758
> 1.850 7.703
> 1.842 1.785
>
> min 1.728 1.785
> avg 1.863 5.979
> max 2.079 8.151
> range 0.351 6.366
>
> The average latency is 3X worse in uClinux, the worst-case
> latency is 4X worse, and the range is 20X worse. We'd like to
> be able to use uClinux for it's better support of wireless and
> wider availability of application code, but the large and
> variable latency times are giving us pause.
>
> I tried using real-time scheduling of the user threads, but it
> didn't help latency and it completely ruined TCP throughput for
> cases where multiple threads were receiving data.
>
> Can anybody provide any hints on what I can do to improve the
> latency under uClinux?
>
> I'm currently using 2.6.26-rc6. What kernel configuration
> parameters should I be looking at?
>
>
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