Messages in this thread | | | Date | Wed, 5 Aug 2020 15:40:02 +0200 | From | peterz@infradea ... | Subject | Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting |
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On Mon, Aug 03, 2020 at 09:22:53PM +0200, Thomas Gleixner wrote:
> totaltime = irqtime + tasktime > > Ignoring irqtime and pretending that totaltime is what the scheduler > can control and deal with is naive at best.
Well no, that's what we call system overhead and is assumed to be included in the 'error margin'.
The way things are set up is that we say that, by default, RT tasks can consume 95% of cputime and the remaining 5% is sufficient to keep the system alive.
Those 5% include all system overhead, IRQs, RCU, !RT workqueues etc..
Obviously IRQ_TIME accounting changes the balance a bit, but that's what it is. We can't really do anything better.
Apparently this SoC has significant IRQ time for some reason. Also, relying on RT throttling for 'correct' behaviour is also wrong. What needs to be done is find who is using all this RT time and why, that isn't right.
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