Messages in this thread | | | Date | Fri, 21 Dec 2001 09:19:04 -0800 (PST) | From | Davide Libenzi <> | Subject | Re: [RFC] Scheduler issue 1, RT tasks ... |
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On Fri, 21 Dec 2001, Mike Kravetz wrote:
> On Thu, Dec 20, 2001 at 02:57:55PM -0800, Davide Libenzi wrote: > > On 21 Dec 2001, Momchil Velikov wrote: > > > > > > I'd like to second that, IMHO the RT task scheduling should trade > > > throughput for latency, and if someone wants priority inversion, let > > > him explicitly request it. > > > > No a great performance loss anyway. It's zero performance loss if the CPU > > that has ran the woke up RT task for the last time is not running another > > RT task ( very probable ). If the last CPU of the woke up task is running > > another RT task a CPU discovery loop ( like the current scheduler ) must > > be triggered. Not a great deal anyway. > > Some time back, I asked if anyone had any RT benchmarks and got > little response. Performance (latency) degradation for RT tasks > while implementing new schedulers was my concern. Does anyone > have ideas about how we should measure/benchmark this? My > 'solution' at the time was to take a scheduler heavy benchmark > like reflex, and simply make all the tasks RT. This wasn't very > 'real world', but at least it did allow me to compare scheduler > overhead in the RT paths of various scheduler implementations.
Mike, a better real world test would be to have a variable system runqueue load with the wakeup of an rt task and measuring the latency of the rt task under various loads. This can be easily implemented with cpuhog ( that load the runqueue ) plus the LatSched ( scheduler latency sampler ) that will measure the exact latency in CPU cycles.
- Davide
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