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

[Wangnan (F)]

On 2016/3/23 17:50, Peter Zijlstra wrote:
> 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.

There are some numbers. You can find them from:

http://lkml.iu.edu/hypermail/linux/kernel/1601.2/03966.html

Thank you.