linux-kernel - Re: [RFC] sched/core: Don't schedule threads on pre-empted vcpus

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Date:   Fri, 4 May 2018 11:47:16 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Rohit Jain <rohit.k.jain@...cle.com>
Cc:     matt@...eblueprint.co.uk, mingo@...nel.org,
        dhaval.giani@...cle.com, subhra.mazumdar@...cle.com,
        steven.sistare@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC] sched/core: Don't schedule threads on pre-empted vcpus

On Wed, May 02, 2018 at 01:52:10PM -0700, Rohit Jain wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 5e10aae..75d1ecf 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4033,6 +4033,9 @@ int idle_cpu(int cpu)
>  		return 0;
>  #endif
>  
> +	if (vcpu_is_preempted(cpu))
> +		return 0;
> +
>  	return 1;
>  }

Basically OK with this, but did you consider idle_cpu() usage outside of
select_idle_sibling()?

For instance, I think got_nohz_idle_kick() isn't quite right with this
on. Similarly for scheduler_tick(), that wants the actual idle state.