Re: [PATCH 1/2] perf: ignore LBR and offcore_rsp.

Andi Kleen
2014-06-23T15:56:44Z

Peter Zijlstra <peterz@infradead.org> writes:

>
> So I really hate this patch, it makes the code hideous. Also, its a
> death by a thousand cuts adding endless branches in this code.

FWIW compared to the cost of a RDMSR (which is a very complex operation
for the CPU) the cost of a predicted branch is nearly in the noise.

>
> Also, the offcore part is retarded, just make sure extra_reg isn't set.
>
> As to the LBR, just make it so that we avoid calling the LBR code to
> begin with; ideally without adding extra code to fast paths.

You mean check once at initialization time.

I'm not sure that would handle all cases unfortunately.