Hi,
On Thu, 2018-11-29 at 15:25 -0800, Eric Dumazet wrote:
>
> On 11/29/2018 03:00 PM, Paolo Abeni wrote:
> > This header define a bunch of helpers that allow avoiding the
> > retpoline overhead when calling builtin functions via function pointers.
> > It boils down to explicitly comparing the function pointers to
> > known builtin functions and eventually invoke directly the latter.
> >
> > The macro defined here implement the boilerplate for the above schema
> > and will be used by the next patches.
> >
> > Suggested-by: Eric Dumazet <Eric Dumazet <eduma...@google.com>
Oops... typo here. For some reasons checkpatch did not catch it.
> > Signed-off-by: Paolo Abeni <pab...@redhat.com>
> > ---
> > include/linux/indirect_call_wrapper.h | 77 +++++++++++++++++++++++++++
> > 1 file changed, 77 insertions(+)
> > create mode 100644 include/linux/indirect_call_wrapper.h
> >
> > diff --git a/include/linux/indirect_call_wrapper.h
> > b/include/linux/indirect_call_wrapper.h
> > new file mode 100644
> > index 000000000000..57e82b4a166d
> > --- /dev/null
> > +++ b/include/linux/indirect_call_wrapper.h
> > @@ -0,0 +1,77 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _LINUX_INDIRECT_CALL_WRAPPER_H
> > +#define _LINUX_INDIRECT_CALL_WRAPPER_H
> > +
> > +#ifdef CONFIG_RETPOLINE
> > +
> > +/*
> > + * INDIRECT_CALL_$NR - wrapper for indirect calls with $NR known builtin
> > + * @f: function pointer
> > + * @name: base name for builtin functions, see
> > INDIRECT_CALLABLE_DECLARE_$NR
> > + * @__VA_ARGS__: arguments for @f
> > + *
> > + * Avoid retpoline overhead for known builtin, checking @f vs each of them
> > and
> > + * eventually invoking directly the builtin function. Fallback to the
> > indirect
> > + * call
> > + */
> > +#define INDIRECT_CALL_1(f, name, ...)
> > \
> > + ({ \
> > + f == name ## 1 ? name ## 1(__VA_ARGS__) : \
>
> likely(f == name ## 1) ? ...
Thank you for the feedback!
I thought about the above, and than I avoided it, because I was not
100% it would fit cases (if any) where we have 2 or more built-in
equally likely.
I guess we can address such cases if and when they will pop-up. I'll do
some more benchmarks with the branch prediction hints, and then if
there are no surprises, I'll add them in v1.
BTW I would like to give the correct attribution here. Does 'Suggested-
by' fit? should I list some other guy @google?
Thanks,
Paols
