Re: [PATCH] Avoid moving tasks when a schedule can be made.

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Ingo Molnar wrote:
* Nick Piggin <[email protected]> wrote:


What I am talking about is when you want a task to have the highest possible scheduling priority and you'd like to guarantee that it is not interrupted for more than Xus, including scheduling latency.


this is not a big issue in practice, because it's very hard to saturate current x86 systems running the -rt kernel with pure IRQ load. The APIC messages all have a natural latency, which serves as a throttler.


Either way, you don't measure it. Doesn't matter. As I said, off topic.


Then it is a fine hack for the RT kernel (or at least an improved, batched version of the patch). No arguments from me.


no, it is also fine for the mainline scheduler, as long as the patch is clean and does the obviously right thing [which the current patch doesnt offer]. A 1+ msec latency with irqs off is nothing to sniff at. Trying

If it were generated by some real workload that cares, then I would care.

to argue that 'you can get the same by using rwsems so why should we bother' is pretty lame: rwsems are rare and arguably broken in behavior, and i'd not say the same about the scheduler (just yet :-).


I don't think it is lame at all. They're fairly important in use in mmap_sem
that I know of. And I have seen workloads where the up_write path gets really
expensive (arguably more relevant ones than hackbench).

PS. I'd like to see you argue how they're broken in behaviour, and how
you're going to replace mmap_sem -- this is not a rhetorical statement,
I'd really be interested to see ;)

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