Re: Real-Time Preemption, -RT-2.6.12-final-V0.7.50-24

[William Weston <weston@sysex.net>]

On Sun, 3 Jul 2005, Ingo Molnar wrote:

> ok, found a bug that could explain the situation: mutex sleeps+wakeups 
> were incorrectly credited as 'interactive sleep' periods, causing the dd 
> processes to be boosted incorrectly. The dd processes created a workload 
> in which they blocked each other in such a pattern that they got boosted 
> periodically, starving pretty much every other task.
> 
> the fix is significant and affects alot of workloads, and should further 
> improve interactivity in noticeable ways. I'm not 100% sure it solves 
> all the starvation problems (e.g. how could normal-prio dd tasks starve 
> the SCHED_FIFO irq threads that drove SysRq?), but the results so far 
> look promising.
> 
> i've uploaded the -50-45 patch, can you under this kernel trigger a 
> 'meltdown' on your SMT box?

Still looking into this issue on -51-06.  Found something really odd:  
SCHED_NORMAL tasks will start to inherit the priority value of some other
SCHED_FIFO task.  If JACK is started at a given SCHED_FIFO priority, X and
all of its children will inherit the same priority value after login.  
Other random processes will inherit this, too -- sometimes init...

SCHED_NORMAL tasks suddenly inheriting priority values in the range
normally reserved for SCHED_FIFO could explain at least part of the
meltdown I've been seeing.  Any thoughts?


Cheers,
--ww
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