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Kernel 2.6 Real-Time Benchmarks
An anonymous reader writes "This whitepaper at LinuxDevices.com includes benchmarks comparing the real-time performance of the vers. 2.4 and 2.6 linux kernels, based on LynuxWorks' BlueCat Linux 5.0 beta. The graphs compare the results for average and worst-case measurements of both interrupt response and task switch performance for the two kernels, running on a 1GHz Pentium III under relatively heavy load. Check it out -- there's an enormous improvement. The article also includes a rundown of other features of the new kernel that seem likely to be welcomed by embedded developers."
LKML verified it and I've experienced it personally -- TCQ on IBM Deathstar drives (mine were 60G, the LKML was 120G IIRC) can cause massive fs corruption.
Apparently a queue depth of 8 (the default it seems) is the specific culprit. LKML seems to say that TCQ of 32 works but I've turned it off entirely now.
It's marked experimental for a reason. :-)
Taken from the article you reference:
SO... they compared a RTOS with an (admitedly) non-realtime OS? I'm not surprised at the results.
RedHat markets ELDS as an OS for embedded systems. Not all embedded systems require realtime performance. Heck, even systems that require realtime performance don't always require the level of performance that QNX can deliver. There's a large number of embedded systems for which even plain Linux without any performance enhancements is a good choice.
If you're really looking for a version of Linux that supports hard real time requirements, take a look at something other than ELDS - <shameless plug> TimeSys Linux, for example </shameless plug>
(yes, I am a TImeSys employee)."Great men are not always wise: neither do the aged understand judgement." Job 32:9
It schedules tasks, handles input/output with hardware, allocates storage and memory, manages processes... it's an operating system. Now, it may be more precise to say "Red Hat Linux" or "GNU/Linux", but that doesn't mean that Linux isn't an operating system.
"The price of freedom is eternal vigilance." - Thomas Jefferson
It seems you need "a system means that performs its functions and responds to external, asynchronous events within a specified amount of time". In other words, a real-time OS. Neither Windows nor Linux are real-time OS. There is some patches that aims at making Linux more real-time.
You can use Tron too.
No GNU has been Hurd during the making of this comment.
The Linux kernel was never intented to compete with QNX or any other realtime operating system.
Try RTAI. It's a patch to allow hard realtime performance on GNU/Linux systems.
Turns out these medical types are absolutely freakin' paranoid about their double blind tests.
Think Team A/Team B analysis at the CIA, but in a laboratory setting, it's more like Team A prepares the dosages [placebo versus varying concentrations of the compound in question], then Team B administers it and gathers data without knowing what it is they are administering.
If you have something like Active Directory [or Novell Directory Services], then the Team A Group will have full Read/Write access to the first half of a subject's record [subject's prior medical history, nature of the compound administered, etc.], but no access whatsoever to the second half of a subject's record [data recorded after compound was administered], whereas the Team B Group has no access to the first half of a subject's record, but full Read/Write access to the second half of the patient's record.
If your real time OS has support for something like Active Directory, or Novell Directory Services, or iPlanet, and, of course, if your backend database does, as well, then Team B group members can upload the data they collect directly into the database, without you [the programmer] having to write some kludgy, half-assed daemon or service or whatever to perform the authentication for you.
PS: This sort of thing works well in reverse for routers. If a router [or a switch] is aware of a directory, it can authenticate itself to the directory, then query the directory and download all of its parameters [like Access Control Lists] from the directory. In the past, Cisco has done this sort of thing for their routers vis-a-vis Novell Directory Services and Active Directory, but, like all Cisco products, that stuff is mucho expensive.
PPS: As for the codecs, our surgeons will want a realtime display of the data that is being collected, which means drivers for both video cards and video capture cards, and codecs for displaying that video on screen. Surprisingly enough, there do seem to be a fair number of companies who have released QNX drivers for video capture cards.