On Sun, Mar 07, 2010 at 04:17:08PM +0100, Aurelien Jarno wrote: > On Sat, Mar 06, 2010 at 11:42:51AM +0100, Jerome Vizcaino wrote: > > Package: libc6 > > Version: 2.10.2-6 > > Severity: normal > > > > Hi, > > > > After many tests and research I've come to the conclusion that the float > > variants > > of > > sin/cos (and maybe others) are anormaly slow Debian amd64. > > The performance loss is really impressive (around 8 to 9 times slower). > > I've attached the prog used to make my experiments and used it in the > > following > > cases. > > > > + Lenny-amd64: sinf/cosf is really slow > > + Lenny-i386: float performance is ok (faster than the cos/sin using double) > > + Sid-amd64: sinf/cosf slow > > + Lenny-amd64 using lenny-i386 binary and 32bits libs: float performance is > > OK. > > On amd64, only sincos has an optimized version, sincosf is using the > generic C implementation. On i386, there are optimized version of both > sincos and sincosf > > > + OpenSuse 64 bits (10.3 and 11.1): using the binary compiled on > > lenny-amd64, > > the tests run fine ! > > => The problem is not compiler related. > > > > There seems to be a problem with the way libm is compiled for the amd64 > > architecture on Debian. > > This is why the OpenSuse test was run: the problem is somewhere in the > > compile > > chain or debian specific patches. > > > > The problem is clearly not Debian specific, and is also present > upstream. OpenSuse is probably using a patch to workaround the problem. >
This is confirmed, there using an AMD version of the libm library on x86_64, still coded in C for the sincosf function. A quick an dirty implementation of sincosf in x86_64 assembly gives me a speed around 4% slower than sincos. What kind of performance ratio do you get on SuSe? The solution seems to write each *f function in x86_64 assembly, but that'll probably take time. -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurel...@aurel32.net http://www.aurel32.net -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
