Re: [PATCH net-next v3 0/4] net: mitigate retpoline overhead
From: Paolo Abeni
Date: Sun Dec 16 2018 - 13:55:51 EST
On Sat, 2018-12-15 at 13:23 -0800, David Miller wrote:
> From: Paolo Abeni <pabeni@xxxxxxxxxx>
> Date: Fri, 14 Dec 2018 11:51:56 +0100
> > The spectre v2 counter-measures, aka retpolines, are a source of measurable
> > overhead. 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 .
> > 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
# 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.
diff --git a/include/linux/indirect_call_wrapper.h b/include/linux/indirect_call_wrapper.h
index 7c8b7f4..00d7e8e9 100644
@@ -28,8 +28,8 @@
-#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_SCOPE static