Re: [PATCH] Makefile: set USE_PIC on Linux x86_64 for linking with Git.pm

From: Junio C Hamano <junkio@cox.net>
Date: Jun 28, 2006, 21:24 UTC
Message-ID: <7vbqsdynvu.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <20060628190814.GC5713@fiberbit.xs4all.nl>

Marco Roeland <marco.roeland@xs4all.nl> writes:

> Even for Linux someone mentioned that probably i386 is the exception in
> _not_ needing the -fPIC linkage. It might even be specific to the Perl
> "xs" implementation specifics?

USE_PIC is for pleasing Perly git and nothing else right now.

> So I should have added "Works for me (TM)"! ;-)

That would have been more explicit way to tell me that this is a partial solution and I should solicit help from people on other platforms.

By the way, I had an impression that compiling things with -fPIC when not necessary was generally a bad idea from performance point of view. If that is the case we might want to compile, under USE_PIC, everything with -fPIC in a separate area to compile and link with Git.xs, without affecting the C-only core code.

I suspect this would largely depend on the architecture. I ran git-fsck-objects compiled with and without -fPIC (after "make clean" to rebuild everything) on a fully packed copy of the linux-2.6 repository on my x86_64 box, and did not see meaningful differences:

: gitster; /usr/bin/time ../git.junio/git-fsck-objects-no-pic --full 109.71user 5.01system 1:54.89elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (14major+1834967minor)pagefaults 0swaps : gitster; /usr/bin/time ../git.junio/git-fsck-objects-with-pic --full 109.05user 4.97system 1:54.08elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+1834981minor)pagefaults 0swaps : gitster;