On Mon, Oct 9, 2023 at 10:36 AM Yajun Deng <yajun.deng@xxxxxxxxx> wrote: > > > 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))++; > I think you are very confused. You only want to trace netdev_core_stats_inc() entry point, not arbitrary pieces of it.
