Date: Tue, 25 Jan 2011 23:49:11 -0500 From: Alexander Kabaev <kabaev@gmail.com> To: Mark Saad <nonesuch@longcount.org> Cc: freebsd-hackers@freebsd.org Subject: Re: rtld optimizations Message-ID: <20110125234911.223d8f75@kan.dnsalias.net> In-Reply-To: <AANLkTikwHteyqMfMpy_B-AxQ5ZQ_Z3RKhkNpGN23fXtX@mail.gmail.com> References: <AANLkTikwHteyqMfMpy_B-AxQ5ZQ_Z3RKhkNpGN23fXtX@mail.gmail.com>
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[-- Attachment #1 --] On Tue, 25 Jan 2011 21:40:42 -0500 Mark Saad <nonesuch@longcount.org> wrote: > Hello Hackers > > The NetBSD folks have a nice improvement with the rtld-elf subsystem, > known as "Negative Symbol Cache" . > > http://blog.netbsd.org/tnf/entry/netbsd_runtime_linker_gains_negative > > Roy Marples roy@ has a simple write up of the change. > > I took the basic idea from FreeBSD, but improved the performance > drastically. Basically, the huge win is by caching both breadth and > depth of the needed/weak symbol lookup. > Easiest to think of a,b,c,d as a matrix and FreeBSD just cache a row > where we cache both rows and columns. > > Has anyone looked into porting the changes back to FreeBSD ? The > improvement on load time for things like firefox, openoffice, and java > is huge on NetBSD. It looks like this change could improve load times > on FreeBSD in the same ways. > This is a second time someone posts this to public mailing list and curiously enough is a second time it suggested that someone else is to do the investigation. From the quick look, the commit in question is more or less a direct rip-off of Donelists we had for ages and as such is completely over-hyped. The only extra quirk that said commit does is an optimization of a dlsym() call, which is hardly ever in critical performance path. Said optimization is trivial and easy to try. Here you have it: http://people.freebsd.org/~kan/rtld-symlook-depth.diff Since it only applies to dlsym, it only affects programs that are heavy plugin users, which I suppose is the category OpenOffice and firefox both fall into. Care to do some benchmarks with and without the patch and report the results? I frankly doubt that you'll see any noticeable difference compared to our stock rtld's performance. -- Alexander Kabaev [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (FreeBSD) iD8DBQFNP6fMQ6z1jMm+XZYRApDcAJ9Qo4tdIl4xVxTwK+k61vAWxX7ZFwCeJNbs 9Bha2Y0q9hEBtn/L7WpwA2E= =0nHC -----END PGP SIGNATURE-----
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