Re: [RFC PATCH 1/3] sched/core: add API for exporting runqueue clock

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Dec 18, 2019 at 03:19:40PM +0800, Ming Lei wrote:
> Scheduler runqueue maintains its own software clock that is periodically
> synchronised with hardware. Export this clock so that it can be used
> by interrupt flood detection for saving the cost of reading from hardware.

But you don't have much, if any, guarantees the thing gets updated.

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 90e4b00ace89..03e2e3c36067 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -219,6 +219,11 @@ void update_rq_clock(struct rq *rq)
>  	update_rq_clock_task(rq, delta);
>  }
>  
> +u64 sched_local_rq_clock(void)
> +{
> +	return this_rq()->clock;
> +}
> +EXPORT_SYMBOL_GPL(sched_local_rq_clock);

Also, more NAK, you're exporting a variant of __rq_clock_broken().

(which, now that I git-grep for it, has become unused, good!)