Re: [PATCH 3/5] perf core: Prepare writing into ring buffer from end

[Peter Zijlstra]

On Mon, Mar 14, 2016 at 09:59:43AM +0000, Wang Nan wrote:
> Convert perf_output_begin to __perf_output_begin and make the later
> function able to write records from the end of the ring buffer.
> Following commits will utilize the 'backward' flag.
> 
> This patch doesn't introduce any extra performance overhead since we
> use always_inline.

So while I agree that with __always_inline and constant propagation we
_should_ end up with the same code, we have:

$ size defconfig-build/kernel/events/ring_buffer.o.{pre,post}
   text    data     bss     dec     hex filename
   3785       2       0    3787     ecb defconfig-build/kernel/events/ring_buffer.o.pre
   3673       2       0    3675     e5b defconfig-build/kernel/events/ring_buffer.o.post

The patch actually makes the file shrink.

So I think we still want to have some actual performance numbers.