RTLinux Boasts Single-Digit uSec Responsiveness

An anonymous reader writes "A Linux implementation delivering single-digit microsecond responsiveness on 64-bit dual-core AMD Opteron processors is being demonstrated at the Embedded Systems Conference in Boston this week. From the article: "According to FSMLabs, an AMD Opteron 265 dual-core system running RTLinux can deliver guaranteed interrupt latencies of no more than five microseconds, with scheduling jitter of no more than eight microseconds, even with Linux under a heavy load." Heck, with numbers like that it seems like Linux could run circles around XP Pro for audio/video apps such as streaming, recording, and playback!"

Comments

beos

[itzdandy]

beos did not handle media well because of low latencies, it handled media well because of thoughtful media system design. beos actually has poor latencies and response times in a number of areas, it just accelled at scheduling and prioritisation

For the love of Christ people, it's a RTOS

[typical]

Okay, I'm going to clear this up near the top of the article.

RTLinux is a *Real Time Operating System*, a tiny kernel that runs the Linux kernel. It has a rather sexy interfact that allows you to write the non-RT code that interacts with it in the regular, Linux way. You also don't need to hassle with Wind River salesmen to use it. This makes it good.

There seems to be a significant misperception here as to what an RTOS is, and the extremely misleading article summary makes it worse.

An RTOS is an extremely specific tool designed to allow someone to write code with very harsh restrictions on it with very low latency. This is almost always used for control applications (telling servos when to fire accurately). You can't "run Quake in RTLinux" and just get more accurate times -- code running as real-time in RTLinux can do very little besides memory manipulation, basic computation, and some extremely limited I/O. RTOSes are powerful tools for solving a very limited set of problems which very few people on Slashdot have.

RTLinux lets you write very simple, limited code that runs in a real-time mode, and run it on the same machine as regular Linux applications. And communicate with them. That's it. Doesn't do anything to improve the regular ol' Linux applications.

RTOSes give very low latency to the code they run -- something happens, code to handle it gets fired off very quickly. Microsecond latency (*not* millisecond) is completely overkill for the kind of general-purpose video or whatever work that people here are thinking of, unless you're trying to build some sort of specialized embedded system that does something to a real-time feed -- and your hardware's going to be very specially designed for this.

There's a good reason that we don't use RTOSes in day-to-day work. They have bad throughput, and you can't *do* very much with them in real-time. They're good if you specifically have a latency constraint from the time one sensor triggers to the time I/O goes out to another device. They aren't going to avoid audio dropouts on your GNOME desktop. Real-time is a *bad thing* from most people's standpoint -- oh, and they're really easy to accidentally hang.

If you want something to get excited about for general purpose use, look at the preempt patches for 2.6. 2.6 Linux has better latency than Windows XP (2.4 had worse). This is not RTLinux, this is regular-ol-Linux-which-can-run-Quake. My understanding is that ALSA and JACK represent improvements in the general-purpose latency area.

Unless you are designing application logic for robotic control systems, or are interfacing with PLCs, RTLinux really doesn't benefit you (okay, I'm sure there's someone out there that has a different application, but Joe Hacker with his Gentoo box doesn't benefit directly from this).

Every time realtime systems come up on Slashdot, misperceptions of 'em seem to get worse.