linux-kernel - [CONFIG_PREEMPT_RT] High frequency periodic timer

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:	Mon, 02 Jul 2007 15:18:12 +0200
From:	John Sigler <linux.kernel@...e.fr>
To:	linux-kernel@...r.kernel.org
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>
Subject: [CONFIG_PREEMPT_RT] High frequency periodic timer

Hello everyone,

I have been experimenting with the CONFIG_PREEMPT_RT patch for a few 
months. Specifically kernel 2.6.20.7-rt8.

http://rt.wiki.kernel.org/index.php/Main_Page

I've been running into some unexpected problems, so I wanted to ask 
those who have some experience with this patch what they thought.

Here's a brief description of my application:

System A periodically sends timestamped packets. These packets travel 
over a network, or through a network emulator, and get randomly dropped 
or delayed by a random amount of time. These packets reach system B at 
some point. System B uses the timestamp to re-send the packets smoothly, 
as if they had been produced on B, with only a constant time-shift. 
Basically, B acts as a "dejittering" router.

I have implemented this with high-resolution timers. Every time the 
timer fires, I send one packet. In "parallel", I buffer incoming packets 
that arrive from system A.

Consider 1316-byte packets and a 80 Mbit/s stream bit rate.

This means the timer period is 1316*8 / 80 = 131.6 µs

I've been wondering whether having such a small period (high frequency) 
might be a problem / challenge for the real-time kernel (scheduler, IRQ 
handler, other component).

The CPU used is mid-range (i.e. 1.5 GHz Celeron M) single core, and it 
easily copes with just the receiving part.

But I have seen some odd behavior (random crashes in my program) that 
must mean I have made some incorrect assumptions.

What do you all think?

Regards.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/