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

Andrew Morton
2006-05-13T12:30:40Z

(Catching up on lkml)

On Thu, 11 May 2006 17:04:11 -0700
"Chen, Kenneth W" <kenneth.w.chen@intel.com> wrote:

> Tim Chen writes:
> > See patch:
> > http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=e72ff0bb2c163eb13014ba113701bd42dab382fe
>
> Con Kolivas wrote on Monday, May 08, 2006 5:43 PM
> > This patch corrects a bug in the original code which unintentionally dropped
> > the priority of tasks that were idle but were already high priority on other
> > merits. It doesn't further increase the priority.
>
>
> This got me to take a non-casual look at that particular git commit. The
> first portion of the change log description says perfectly about the intent,
> but after studying the code, I have to say that the actual code does not
> implement what people say it will do. In recalc_task_prio(), if a task's
> sleep_time is more than INTERACTIVE_SLEEP, it will bump up p->sleep_avg all
> the way to near maximum (at MAX_SLEEP_AVG - DEF_TIMESLICE), which according
> to my calculation, it will have a priority bonus of 4 (out of max 5).
>
> IOW, for a prolonged sleep, a task will immediately get near maximum priority
> boost. Is that what the real intent is? Seems to be on the contrary to what
> the source code comments as well.
>
> I think in the if (sleep_time > INTERACTIVE_SLEEP) block, p->sleep_avg should
> be treated similarly like what the "else" block is doing: scale it proportionally
> with past sleep time, perhaps not the immediate previously prolonged sleep
> because that would for sure bump up priority too fast. A better method might
> be p->sleep_avg *= 2 or something like that.
>

That seems to be a pretty significant discovery. Is anything happening
with it?