Re: [RFC PATCH v2 2/3] restartable sequences: x86 ABI

[Peter Zijlstra]

On Tue, Oct 27, 2015 at 04:57:05PM -0700, Paul Turner wrote:
> +static void rseq_sched_out(struct preempt_notifier *pn,
> +			   struct task_struct *next)
> +{
> +	set_thread_flag(TIF_NOTIFY_RESUME);
> +}
>  
>  static __read_mostly struct preempt_ops rseq_preempt_ops = {
>  	.sched_in = rseq_sched_in_nop,
> -	.sched_out = rseq_sched_out_nop,
> +	.sched_out = rseq_sched_out,
>  };

Since we're unconditionally setting this TIF flag for these tasks, can't
we introduce something similar to the (contested) TIF_NOHZ_FULL thing
which is kept on the task indefinitely.

That avoids having the preempt notifiers and this atomic op in the
schedule path.
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