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

[Ingo Molnar <mingo@elte.hu>]

* Nick Piggin <nickpiggin@yahoo.com.au> wrote:

> >rwsems/rwlocks are not an issue in -rt because they have different 
> >semantics there - and thus readers cannot amass. I do think rwsems and 
> >rwlocks have pretty nasty characteristics [non-latency ones] for the 
> >mainline kernel's use too, but that's not being argued here ;)
> 
> But all I'm saying is that while there are equivalent magnitudes of 
> interrupts off regions in mainline, there is little point introducing 
> a hack like this to "solve" one of them.

nobody is arguing to have this hack included. Hacks are to be introduced 
into the scheduler only over my cold dead body ;-) Steve only sent this 
as an RFC thing, to raise the issue.

> If anyone is running hackbench 20 on their sound mixer, then they 
> deserve to have overruns.

just to give you an idea of what we have achieved with the -rt kernel so 
far: my regular -rt stress-test setup has a "hackbench 50" in its 
"deadly mix of SCHED_OTHER workloads", in addition to 40 parallel runs 
of LTP runalltests.sh, with flood pinging and other networking and IO 
stresstests, combined with a task that allocates and dirties a 1.5GB 
buffer in an infinite loop while there's only 1GB of RAM - and still 
during many hours of running this stress-test (which produces a load 
average of 200-500) the -rt kernel runs SCHED_FIFO tasks in 20 usecs, 
worst-case.

	Ingo
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