Overview of Linux real-time challenges

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Overview of
Linux
realtime
challenges
June 1, 2013

Daniel Stenberg
Email: daniel@haxx.se
Twitter: @bagder
Web: daniel.haxx.se
Blog: daniel.haxx.se/blog
●
Free Software
●
Net...

Agenda
What's real-time in this context?
Why is real-time still a concern?
Ways to deal with the problem
• Off to secondar...

Realtime
Real-time can mean a lot of different
things to different audiences
• Low maximum latency: below 100 us,
sometim...

Why is this a concern
2013?
• Plain Linux wasn't designed to deal with low latency
• A move towards "commodity" hardware ...

What are the options?
Linux is a given.
What magic can you apply to a system
to address the problem of a low
maximum laten...

Separate dedicated HW
• A tested and proven way
• A separate small chip (with an
RTOS?) for just the time critical stuff
•...

Hypervisor with RTOS
• Isn't pure Linux
• Adds complexity
• Usually proprietary
• May reach really low latencies
One or mo...

AMP with RTOS
• Isn't pure Linux
• Adds complexity
• Often proprietary
• May reach really low latencies
Core 0 Core 1 Core...

The more pure Linux
solutions
1 Address and lower the worst
case
2 Avoid hitting the worst case

PREEMPT_RT
●
An offmainline patch since 10+ years!
●
Add preemption to lower max latency
●
replace kernel spinlocks with ...

CPU isolation 1/2
●
NOHZ, dynamic tick
●
Isolated cores == without ticks do nothing!
●
Only one thread allowed!
●
Avoiding...

Linux kernel
Core 0 Core 1 Core 2 Core 3
CPU isolation 2/2

Future
●
Realtime and latency remain
interesting
●
PREEMPT_RT is not in mainline
●
NOHZ is just getting in
●
We create t...

(from UBM Tech Electronics' Embedded Market Survery)

Work with this at Enea

Thank you
Daniel Stenberg <daniel@haxx.se>

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