Re: [PATCH] trace: adjust code layout in get_recursion_context

[Peter Zijlstra]

On Tue, Aug 22, 2017 at 04:40:24PM +0200, Jesper Dangaard Brouer wrote:
> In an XDP redirect applications using tracepoint xdp:xdp_redirect to
> diagnose TX overrun, I noticed perf_swevent_get_recursion_context()
> was consuming 2% CPU. This was reduced to 1.6% with this simple
> change.

It is also incorrect. What do you suppose it now returns when the NMI
hits a hard IRQ which hit during a Soft IRQ?

> @@ -208,12 +208,12 @@ static inline int get_recursion_context(int *recursion)
>  {
>  	int rctx;
>  
> +	if (in_softirq())
> +		rctx = 1;
>  	else if (in_irq())
>  		rctx = 2;
> +	else if (in_nmi())
> +		rctx = 3;
>  	else
>  		rctx = 0;
>  
>