Re: [RFC][PATCH 1/5] sched/fair: Fix select_idle_cpu()s cost accounting

[Peter Zijlstra]

On Fri, Jan 08, 2021 at 04:10:51PM +0100, Vincent Guittot wrote:
> Another thing that worries me, is that we use the avg_idle of the
> local cpu, which is obviously not idle otherwise it would have been
> selected, to decide how much time we should spend on looking for
> another idle CPU. I'm not sure that's the right metrics to use
> especially with a possibly stalled value.

The thinking was that if this CPU has little idle time, this CPU should
not spend a lot of time searching...

That is; if we spend more time looking for places to run, than we have
idle time, we're loosing cycles we could've ran (supposedly useful) work.

The only counter argument is tail latency.