From mboxrd@z Thu Jan  1 00:00:00 1970
From: Neil T. Dantam <ntd@gatech.edu>
Date: Mon, 21 Oct 2013 17:41:00 -0400
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Subject: [Xenomai] Slow Sockets and Pipes with POSIX Skin
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To: xenomai@xenomai.org

I am seeing some surprisingly high latencies for socket and pipe
communication using Xenomai's POSIX skin.  Pipes, localhost TCP/UDP,
and local domain sockets all show worst case latency of ~100us on
Xenomai 2.6.2.1/Linux 3.4.6 on a Xeon E3-1270v2.  Average and 99%
latency is under 20us.  Running `xeno-test latency` gives worst-case
latency of ~10us.  POSIX message queues have worst case latency below
20us.

I've done the following to reduce latency:

* Disabled CPU frequency scaling
* Disabled USB
* Set real-time scheduling priority
* Prefaulted the stack

The 100us delay seems like what one get from a System Management
Interrupt (SMI).  However, since `xeno-test latency` and message
queues both show low latency, it seems unlikely that this could be the
issue.

Has anyone else encountered (or not encountered) similar performance
issues with pipes and sockets?

Cheers,
-ntd