Re: [PATCH net-next v7] net/core: Introduce netdev_core_stats_inc()

[Eric Dumazet <edumazet@google.com>]

On Mon, Oct 9, 2023 at 10:14 AM Yajun Deng <yajun.deng@linux.dev> wrote:
>
>
> On 2023/10/9 15:53, Eric Dumazet wrote:
> > On Mon, Oct 9, 2023 at 5:07 AM Yajun Deng <yajun.deng@linux.dev> wrote:
> >
> >> 'this_cpu_read + this_cpu_write' and 'pr_info + this_cpu_inc' will make
> >> the trace work well.
> >>
> >> They all have 'pop' instructions in them. This may be the key to making
> >> the trace work well.
> >>
> >> Hi all,
> >>
> >> I need your help on percpu and ftrace.
> >>
> > I do not think you made sure netdev_core_stats_inc() was never inlined.
> >
> > Adding more code in it is simply changing how the compiler decides to
> > inline or not.
>
>
> Yes, you are right. It needs to add the 'noinline' prefix. The
> disassembly code will have 'pop'
>
> instruction.
>

The function was fine, you do not need anything like push or pop.

The only needed stuff was the call __fentry__.

The fact that the function was inlined for some invocations was the
issue, because the trace point
is only planted in the out of line function.