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Re: performance loss on real time linux

Dieter Kluenter wrote:
I am at an early stage of deploying OpenLDAP running on Monstavista
Carrier Grade linux, with Linux-2.6 kernel but modified scheduler.
For this I compiled and installed OpenLDAP-2.3.27 on my TP T43
notebook and on a x86 Carrier Grade hardware, I'm not sure about the
processor manufacturer and type of this hardware.
On both machines identical DB_CONFIG files, slapd.conf and data have
been set up. I created only 10,000 entries as this would the expected
average database size be.
A ldapsearch on localhost with SuSE-9.3 Linux, after some warming
up the results were levelling at

real    0m0.010s
user    0m0.002s
sys     0m0.003s

with Montavista

real    0m0.827s
user    0m0.014s
sys     0m0.015s

Due to a real time scheduler I was expecting the results to be vice
Can a RT scheduler or other modifications to the operating system have
a negative influence on performance of OpenLDAP?

You can't expect results to be any better than under non-RT os, since a RT-scheduler will always add overhead to non-RT processes since it will preempt much more than a normal OS. I have no experience with Monta-Vista, however my institution (Politecnico di Milano) develops RTAI, the Real-Time Application Interface for Linux (http://www.rtai.org/); I'll check what happens when running OpenLDAP with that.

In the meanwhile, can you tell something more about Monta Vista's handling of RT? Does it include the PREEMPT_RT patch, which will likely become part of Linux in a year or so, or does it rather implement some custom support to handle preemption?

About your test: are your results an average over a realistic number of trials? Is the database entirely in cache or does it require any access to disk? Mallocs under a real-time scheduler might also represent a significant bottleneck; in this case, slapd should really handle memory internally, to minimize the amount of system calls.


Ing. Pierangelo Masarati
OpenLDAP Core Team

SysNet s.n.c.
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Email:    pierangelo.masarati@sys-net.it