Messages in this thread | | | Date | Sat, 10 Jul 2004 13:15:28 +0200 | From | Ingo Molnar <> | Subject | Re: Likelihood of rt_tasks |
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* Con Kolivas <kernel@kolivas.org> wrote:
> Well I dont think making them unlikely is necessary either, but > realistically the amount of time added by the unlikely() check will be > immeasurably small in real terms - and hitting it frequently enough > will be washed over by the cpu as Ingo said. I dont think the order of > magnitude of this change is in the same universe as the problem of > scheduling latency that people are complaining of.
very much so. This is (sub-)nanoseconds stuff, while the scheduling latencies are tens of milliseconds or more - at least 7 orders of magnitude difference.
the unlikely() check in rt_task() was mainly done because there was a steady stream of microoptimizations that added unlikely() to rt_task(). So now we do in everywhere and have removed the unlikely()/likely() branches from sched.c. It doesnt really matter in real-world terms, but it will make the common case code (non-RT) a tiny bit more compact. And i challenge anyone to be able to even measure the difference to an RT task.
Not to mention that any truly RT-centric/embedded distribution would compile the kernel for size anyway, at which point the compiler ignores (or should ignore) the likely/unlikely attributes anyway. So there's really no harm to anyone and the code got a bit more readable.
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