Date: Fri, 11 Mar 2011 13:06:47 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Martin Matuska <mm@freebsd.org> Cc: freebsd-performance@freebsd.org, freebsd-current@freebsd.org Subject: Re: FreeBSD Compiler Benchmark: gcc-base vs. gcc-ports vs. clang Message-ID: <20110311110647.GN78089@deviant.kiev.zoral.com.ua> In-Reply-To: <4D7943B1.1030604@FreeBSD.org> References: <4D7943B1.1030604@FreeBSD.org>
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[-- Attachment #1 --] On Thu, Mar 10, 2011 at 10:33:37PM +0100, Martin Matuska wrote: > Hi everyone, > > we have performed a benchmark of the perl binary compiled with base gcc, > ports gcc and ports clang using the perlbench benchmark suite. > Our benchmark was performed solely on amd64 with 10 different processors > and we have tried different -march= flags to compare binary performance > of the same compiler with different flags. > > Here is some statistics from the results: > - clang falls 10% behind the base gcc 4.2.1 (test average) > - gcc 4.5 from ports gives 5-10% better average performance than the > base gcc 4.2.1 > - 4% average penalty for Intel Atom and -march=nocona (using gcc from base) > - core i7 class processors run best with -march=nocona (using gcc from base) > > This benchmark speaks only for perl, but it tests quite a lot of > "generic" features so we a are seriously considering using ports gcc for > heavily used ports (e.g. PHP, MySQL, PostgreSQL) and suggesting that an > user should be provided with a easily settable choice of using gcc 4.5 > for ports. > > A first step in this direction is in this PR (allowing build-only > dependency on GCC): > http://www.freebsd.org/cgi/query-pr.cgi?pr=ports/155408 > > More information, detailed test results and test configuration are at > our blog: > http://blog.vx.sk/archives/25-FreeBSD-Compiler-Benchmark-gcc-base-vs-gcc-ports-vs-clang.html Putting the 'speed' question completely aside, I would like to comment on other issue(s) there. The switching of the ports to use the port-provided compiler (and binutils) would be very useful and often talked about feature. Your approach of USE_GCC_BUILD as implemented is probably not going to work. The problem is that gcc provides two libraries, libgcc and libstdc++, that are not forward-compatible with the same libraries from older compilers and our base. libstdc++ definitely did grown new symbols and new versions of old symbols, and I suspect that libgcc did the same. Also, we are trusting the ABI stability premise. For this scheme to work, we at least need a gcc-runtime port with dsos provided by full port, and some mechnanism to force the binaries compiled with port gcc to use gcc-runtime libs instead of base. Might be, -R<path> linker cludge. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEARECAAYFAk16AkcACgkQC3+MBN1Mb4iIRwCeIT06hU87Qh6XusOKxwZIcFn1 XaAAoKJYekOQhkw7GDStE8a5cqsLfsd3 =vWaL -----END PGP SIGNATURE-----help
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