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

[Mike Galbraith <efault@gmx.de>]

On Sat, 2006-05-13 at 05:27 -0700, Andrew Morton wrote:
> (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?

When I tried to fix that, I ran into resistance.

	-Mike