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

From: Peter Williams
Date: Wed May 17 2006 - 00:45:20 EST

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?

Peter Williams pwil3058@xxxxxxxxxxxxxx

"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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