> -----Original Message----- > From: Damjan Marion <dmar...@me.com> > Subject: Re: [vpp-dev] clang-9 > > > Dear Lijian, > > I don’t see how this matters if neither gcc 9.2+ or clang-10 are available in > ubuntu 18.04. > For custom builds users can simply say make CC=whatever-compiler-they- > want … Not sure how 'CMAKE_C_COMPILER_NAMES' takes effect, but experiments show "make CC=gcc" can override "set(CMAKE_C_COMPILER_NAMES clang-10 clang-9 gcc-9 cc)" in CMakeLists.txt. It's a good way for custom builds with non-default compiler.
> > Also there is no N1 available in CSIT, so we cannot really judge about > performance impact on the large number of different features. > > — > Damjan > > > On 28 May 2020, at 09:50, Lijian Zhang <lijian.zh...@arm.com> wrote: > > > > Hi Damjan, > > I got some feedback regarding switching default compiler from gcc to clang > in VPP, from compiler team. > > > > " Neither LLVM nor GCC tune much for Neoverse N1, I think the difference is > that GCC has better vectorization and a better optimized AArch64 backend. > GCC10 has just been released and will likely do even better (it is now ~20% > ahead of LLVM on SPEC)." > > > > " I was looking at the roadmap for LLVM (which is the backend for clang). I > see plans for tuning for Zeus and Perseus, but just support for N1. I think > they > fixed some alignment issues and replaced some intrinsics, but no specific N1 > tuning. LLVM is behind gcc in performance, by a decent amount." > > > > I did some benchmarking on L2/L3 single flow throughput btw gcc-9.2.0 (- > march=armv8.2-a+crc+crypto -mtune=neoverse-n1) and clang-10 (- > mcpu=neoverse-n1). From the results below, gcc-9.2.0 gives better throughput > number (about 4%) than clang-10. > > > > clang-10: > > L3: 11.04Mpps/10.99Mpps/11.02Mpps > > L2: 11.55Mpps/11.56Mpps > > > > gcc-9.2.0 > > L3: 11.61Mpps/11.55Mpps/11.59Mpps > > L2: 12.15Mpps/12.16Mpps > > > > Is it possible to restore gcc as the default compiler for vpp, or for vpp > compiling on Arm CPU? > > Is it possible to remove clang-9 dependency in Makefile, or make it applied > for x86 only? > > This dependency forces vpp compiling to use clang-9 always. > > > > diff --git a/Makefile b/Makefile > > ifeq ($(OS_VERSION_ID),18.04) > > DEB_DEPENDS += python-dev python-all python-pip python-virtualenv > > DEB_DEPENDS += libssl-dev > > - DEB_DEPENDS += clang-9 > > diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt > > -set(CMAKE_C_COMPILER_NAMES clang-10 clang-9 gcc-9 cc) > > +set(CMAKE_C_COMPILER_NAMES gcc-9 cc) > > > > Thanks.
-=-=-=-=-=-=-=-=-=-=-=- Links: You receive all messages sent to this group. View/Reply Online (#16596): https://lists.fd.io/g/vpp-dev/message/16596 Mute This Topic: https://lists.fd.io/mt/73327785/21656 Group Owner: vpp-dev+ow...@lists.fd.io Unsubscribe: https://lists.fd.io/g/vpp-dev/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
