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SubjectRe: [BUG] How to get real-time priority using idle priority
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On Sun, 2009-01-11 at 02:58 -0800, Brian Rogers wrote:
> The attached program gives itself idle priority, then forks off two
> child processes that execute a busy loop. The result is that sometimes
> all other processes stop and the whole system freezes until this program
> exits. An affected system will respond to pings, but X freezes, the
> cursor won't move, SSH sessions won't respond or echo characters back,
> and not even a text console will budge. Hitting Alt-SysRq-N twice can
> sometimes unfreeze the system, or you can just wait for the program to exit.
>
> This bug is in 2.6.29-rc1. I have also observed this bug in 2.6.28 on
> two dual-core systems, an Athlon X2 desktop and a Core 2 Duo laptop.
> Both are running a 64-bit system. Using i386 and amd64 Ubuntu Jaunty
> daily builds with a 2.6.28 kernel, I found I could reproduce the problem
> with the 64-bit kernel, but not the 32-bit kernel. Since that might just
> be due to a difference in the kernel configurations, I'm attaching the
> kernel configuration on which I know this problem can be triggered.
>
> It may take a couple-dozen runs of this program for the freeze to occur.
> Just hit control-C and re-run the program until it happens. When it does
> freeze, the effect is immediate, so there's no chance you'll interrupt
> the program too soon.

Hi,

I haven't been able to reproduce complete hangs, but with your proggy
adapted to my quad, _and_ the addition of a SCHED_NORMAL hog, I can
reproduce some very bad interactivity, including massive character
repeats while attempting to type, and general "lurchiness" (_bad_ wakeup
latency). I'll poke it with a sharp stick or two.

-Mike



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