Re: [PATCH 1/3] sched: select_task_rq() should check cpu_active() like select_fallback_rq()

[Peter Zijlstra]

On Sat, Oct 10, 2015 at 08:53:09PM +0200, Oleg Nesterov wrote:
> I do not understand the cpu_active() check in select_fallback_rq().
> x86 doesn't need it, and the recent commit dd9d3843755d "sched: Fix
> cpu_active_mask/cpu_online_mask race" documents the fact that on any
> architecture we can ignore !active starting from CPU_ONLINE stage.
> 
> But any possible reason why do we need this check in "fallback" must
> equally apply to select_task_rq().

So the reason, from vague memory, is that we want to allow per-cpu
threads to start/stop before/after active.

active 'should' really only govern load-balancer bits or so.
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