Re: [REPORT] cfs-v4 vs sd-0.44

[David Lang <david.lang@digitalinsight.com>]

On Tue, 24 Apr 2007, Ingo Molnar wrote:

> * Gene Heskett <gene.heskett@gmail.com> wrote:
>
> > > Gene has done some testing under CFS with X reniced to +10 and the
> > > desktop still worked smoothly for him.
> >
> > As a data point here, and probably nothing to do with X, but I did
> > manage to lock it up, solid, reset button time tonight, by wanting
> > 'smart' to get done with an update session after amanda had started.
> > I took both smart processes I could see in htop all the way to -19,
> > but when it was about done about 3 minutes later, everything came to
> > an instant, frozen, reset button required lockup.  I should have
> > stopped at -17 I guess. :(
>
> yeah, i guess this has little to do with X. I think in your scenario it
> might have been smarter to either stop, or to renice the workloads that
> took away CPU power from others to _positive_ nice levels. Negative nice
> levels can indeed be dangerous.
>
> (Btw., to protect against such mishaps in the future i have changed the
> SysRq-N [SysRq-Nice] implementation in my tree to not only change
> real-time tasks to SCHED_OTHER, but to also renice negative nice levels
> back to 0 - this will show up in -v6. That way you'd only have had to
> hit SysRq-N to get the system out of the wedge.)

if you are trying to unwedge a system it may be a good idea to renice all tasks 
to 0, it could be that a task at +19 is holding a lock that something else is 
waiting for.

David Lang
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