On Sat, 2018-12-15 at 13:23 -0800, David Miller wrote:

From: Paolo Abeni <pabeni@redhat.com>
Date: Fri, 14 Dec 2018 11:51:56 +0100

quoted

The spectre v2 counter-measures, aka retpolines, are a source of measurable
overhead[1]. We can partially address that when the function pointer refers to
a builtin symbol resorting to a list of tests vs well-known builtin function and
direct calls.

Experimental results show that replacing a single indirect call via
retpoline with several branches and a direct call gives performance gains
even when multiple branches are added - 5 or more, as reported in [2].

This may lead to some uglification around the indirect calls. In netconf 2018
Eric Dumazet described a technique to hide the most relevant part of the needed
boilerplate with some macro help.

This series is a [re-]implementation of such idea, exposing the introduced
helpers in a new header file. They are later leveraged to avoid the indirect
call overhead in the GRO path, when possible.

Overall this gives > 10% performance improvement for UDP GRO benchmark and
smaller but measurable for TCP syn flood.

The added infra can be used in follow-up patches to cope with retpoline overhead
in other points of the networking stack (e.g. at the qdisc layer) and possibly
even in other subsystems.

 ...

Series applied, I'll push this out after a build check completes.

Again, I messed it! I'm really sorry to waste everybody's time.
I was unable to give proper coverage with different configs. I tested
vs.:

CONFIG_IPV6=ymn
CONFIG_INET=yn

but

# CONFIG_RETPOLINE is not set

fooled me. The following patch should fix. I'll try more
configurations. Is there any way to try/tests all kbuild robot configs?

Please feel free to give me an hard stop if this sounds too much a
trial and error thing.

Paolo

--

diff --git a/include/linux/indirect_call_wrapper.h b/include/linux/indirect_call_wrapper.h
index 7c8b7f4..00d7e8e9 100644
--- a/include/linux/indirect_call_wrapper.h
+++ b/include/linux/indirect_call_wrapper.h

@@ -28,8 +28,8 @@
 #define INDIRECT_CALLABLE_SCOPE
 
 #else
-#define INDIRECT_CALL_1(f, name, ...) f(__VA_ARGS__)
-#define INDIRECT_CALL_2(f, name, ...) f(__VA_ARGS__)
+#define INDIRECT_CALL_1(f, f1, ...) f(__VA_ARGS__)
+#define INDIRECT_CALL_2(f, f2, f1, ...) f(__VA_ARGS__)
 #define INDIRECT_CALLABLE_DECLARE(f)
 #define INDIRECT_CALLABLE_SCOPE                static
 #endif