Re: SCHED: Is task migration necessary in sched_exec().

From: Peter Zijlstra
Date: Wed Dec 23 2009 - 05:53:33 EST

On Wed, 2009-12-23 at 16:46 +0600, Rakib Mullick wrote:
> On 12/23/09, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Wed, 2009-12-23 at 16:14 +0600, Rakib Mullick wrote:
> >
> >
> > Well, if there's an imbalance the 'slow' load-balancer will move it
> > around eventually anyway, and since it will then have build up a larger
> > cache footprint it will be even more expensive.
> >
> If there is an imbalance - then the overloaded task will moved.

There is no overloaded task, its the runqueue that is overloaded wrt to
other runqueues. The load-balancer has to pick a 'random' task and pray.
Current heuristics try to pick a task that hasn't been on the cpu for a
while, because for those the effective cache footprint is minimal.

> Why the _current_ task?

Because at exec it has effective 0 cache footprint, and is thus an ideal
victim to move about.

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