Re:Real time Linux has one known issue remaining
by chippiewill on Monday February 21, 2022 @09:29AM
(#30416227)
> a missed deadline is either equivalent to a catastrophic error (hard real time) or really terrible but non catastrophic error (soft real time)
I think you're conflating soft/hard real time with criticality (although they're often aligned)
Hard real time refers to a total system failure, even if it has trivial consequences. For example if a printer has a timing error at any point the page it's printing is irrecoverably ruined. It's hard real-time but low criticality.
Soft real time is where you can miss deadlines but the performance / experience degrades rather than fails. e.g. frame rate drops in a video game. The frames are still valid when delivered late, but the experience is poor.
> Slight nit, real time systems are designed for a maximum worst case latency within some spec, not minimum latency.
Indeed, in fact at times you don't even want a substantially lower minimum latency because it may cause unreasonable jitter in your output.
I think you're conflating soft/hard real time with criticality (although they're often aligned)
Hard real time refers to a total system failure, even if it has trivial consequences. For example if a printer has a timing error at any point the page it's printing is irrecoverably ruined. It's hard real-time but low criticality.
Soft real time is where you can miss deadlines but the performance / experience degrades rather than fails. e.g. frame rate drops in a video game. The frames are still valid when delivered late, but the experience is poor.
> Slight nit, real time systems are designed for a maximum worst case latency within some spec, not minimum latency.
Indeed, in fact at times you don't even want a substantially lower minimum latency because it may cause unreasonable jitter in your output.