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

[Yajun Deng]

On 2023/10/9 16:20, Eric Dumazet wrote:
> On Mon, Oct 9, 2023 at 10:14 AM Yajun Deng <yajun.deng@xxxxxxxxx> wrote:
> > On 2023/10/9 15:53, Eric Dumazet wrote:
> > > On Mon, Oct 9, 2023 at 5:07 AM Yajun Deng <yajun.deng@xxxxxxxxx> 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.


But somehow the following code isn't inline? They didn't need to add the 
'noinline' prefix.

+		field = (unsigned long *)((void *)this_cpu_ptr(p) + offset);
+		WRITE_ONCE(*field, READ_ONCE(*field) + 1);

Or
+               (*(unsigned long *)((void *)this_cpu_ptr(p) + offset))++;