Re: Synchronizing user space threads with kernel space in linux

Supposedly the low-latency patch can give worst-case latency of around

150us, but you'd need to check out how this fits on your architecture.

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"Jokes mentioning ducks were considered particularly funny." - cnn.com

Keeps everything nice and simple. There is a consistent way of dealing with hardware.

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"Jokes mentioning ducks were considered particularly funny." - cnn.com

"Mad@Spammers" schrieb:

Look at rtc.c in the Kernel source. They provide a blocking read to the application to have it wait for an event. Her some data is provided to the application, too.

-Michael

Nope. Linux can't guarantee any worst-case latency at all (I did find more than 100 msek with the low-latency patch in very rare instances).

-Michael

That's why I was quite careful not to use the word "guarantee".

Clearly if you need hard real time performance, you need to look at another OS.

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"Jokes mentioning ducks were considered particularly funny." - cnn.com

"Hard real-time means no surprises or silent failures as system configuration changes or load increases. Deadlines will still be met. For example, the worst case delay on a 1 millisecond thread on the HP Pavilion Notebook (AMD K7) is 12 microseconds. -

"RTAI's microkernel approach guarantees that the data-acquisition task will take place on schedule, even while the previously acquired and calculated result is written to disk." -

"Lineo Solutions, Inc. (Lineo) demonstrated ... hard real-time support with Linux .... Deterministic time metrics of the systems demonstrated ... is as follows.

Interrupt Response Time 5 microseconds

Task Latency Time 4 microseconds

Periodic Task Latency Time 20 microseconds

Timer Clock Accuracy 1 microsecond, Jitter 1 microsecond)"

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"RTAI - the Realtime Linux Application Interface for Linux ... lets you write applications with strict timing constraints for your favourite operating system." -

"KURT-Linux: Kansas University Real-Time Linux: Microsecond timing resolution and event-driven real-time scheduling..." -

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"What is RTAI?

RTAI means Real Time Application Interface. Strictly speaking, it is not a real time operating system, such as VXworks or QNX. It is based on the Linux kernel, providing the ability to make it fully pre-emptable. "

Your serve.

[BTW, isn't RTAI a kernel - a microkernel - all by itself ? You could say that this isn't actually Linux. Linux runs essentially as a process above RTAI. This isn't necessary in an OS such as, for example, Greenhills Integrity, which provides guaranteed latency and other goodies.]

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"Jokes mentioning ducks were considered particularly funny." - cnn.com