Re: Regression seen for patch "sched:dont decrease idle sleep avg"

From: Mike Galbraith
Date: Wed May 17 2006 - 01:23:27 EST

On Wed, 2006-05-17 at 14:45 +1000, Peter Williams wrote:
> Mike Galbraith wrote:
> > On Tue, 2006-05-16 at 16:32 -0700, Tim Chen wrote:
> >> On Tue, 2006-05-16 at 09:45 +1000, Con Kolivas wrote:
> >>
> >>> Yes it's only designed to detect something that has been asleep for an
> >>> arbitrary long time and "categorised as idle"; it is not supposed to be a
> >>> priority stepping stone for everything, in this case at MAX_BONUS-1. Mike
> >>> proposed doing this instead, but it was never my intent.
> >> It seems like just one sleep longer than INTERACTIVE_SLEEP is needed
> >> kick the priority of a process all the way to MAX_BONUS-1 and boost the
> >> sleep_avg, regardless of what the prior sleep_avg was.
> >>
> >> So if there is a cpu hog that has long sleeps occasionally, once it woke
> >> up, its priority will get boosted close to maximum, likely starving out
> >> other processes for a while till its sleep_avg gets reduced. This
> >> behavior seems like something to avoid according to the original code
> >> comment. Are we boosting the priority too quickly?
> >
> > The answer to that is, sometimes yes, and when it bites, it bites hard.
> > Happily, most hogs don't sleep much, and we don't generally have lots of
> > bursty sleepers.
> >
> But it's easy for a malicious user to exploit. Yes?

Without limits, sure. Burn malicious idiot's library card :) The real
pain begins when you start examining legitimate loads. It _can_ get
really and truly fugly. Generally doesn't.


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