Should Linux start paying more attention to 64bit ?

[Linuxhippy]

Ubuntu benchmarks often show 64bit performing BEHIND 32bit in some tests.

Why do you conclude that there are problems, just because 64bit performs sometimes worse than 32-bit? Because 64 is more than 32?

64bit means pointers are all 64-bit wide - that means many datastructures grow significantly -> applications use more memory for same data -> less data fits in cache -> more stress on memory subsystem.
Thats the price we have to pay with 64-bit.

After all, the performance improvements in some benchmarks are often not because 64-bit arithemtic operations (SSE2 already does the same), but because there are now 16 instead of 8 registers and PC-relative adressing is now supported.

- Clemens

[Nille]

For everyone this is a nice Article about AMD64 Architecture http://www.bit-tech.net/bits/2007/10...just_the_ram/1

[hmmm]

The only flaw I can see in 64 bit is ndiswrapper for wireless drivers - some of these windows drivers did not come out in a 64 bit verions

[MetalheadGautham]

Why do you conclude that there are problems, just because 64bit performs sometimes worse than 32-bit? Because 64 is more than 32?

64bit means pointers are all 64-bit wide - that means many datastructures grow significantly -> applications use more memory for same data -> less data fits in cache -> more stress on memory subsystem.
Thats the price we have to pay with 64-bit.

After all, the performance improvements in some benchmarks are often not because 64-bit arithemtic operations (SSE2 already does the same), but because there are now 16 instead of 8 registers and PC-relative adressing is now supported.

- Clemens

Well, THAT is a valid issue with 64bit, but isn't it offset by multimedia performance ?

[Linuxhippy]

Well, THAT is a valid issue with 64bit, but isn't it offset by multimedia performance ?

After all, why should "multimedia software" be so much different from other software.
If the software already uses SSE(2) there's nothing to gain here, so the improvements are reduced to 64-bit integer scalar math stuff and more registers.

For everyone this is a nice Article about AMD64 Architecture http://www.bit-tech.net/bits/2007/10...just_the_ram/1

The article is horrible. Its full of half-wishdom and wrong conclusions/assumptions:

1. This type of programming can be very inefficient, as it requires an absolute understanding of which addresses and registers are free at the time. If that for some reason was already full or was otherwise unable to be written, the program would crash due to a general protection fault. It also meant that little program pieces were strewn about free memory addresses and registers rather than intelligently organised.
2. Linux/Unix/BSD users are given a whole different choice. The 'nix universe has developed kernels designed specifically to run only 64-bit
3. .....

1. Why should what crash? The autor seems to mix&match descriptions about pic-code, pdc-code and pc-relative adressing.
2. WTF?

- Clemens

[npcomplete]

The biggest issue I see with Linux 64-bit is that you can't choose between 32-bit and 64-bit libraries by default. That is, you only have one "/usr/lib" and in a 64-bit installation, they're all 64-bit libs. If you have a 32-bit program requiring a lib in /usr/lib, you're screwed.

Solaris for example requires both 32-bit and 64-bit binaries for drivers and libs to be installed together (i.e. the 64-bit version in under the "amd64" or "64" subdir and the system takes care of choosing the right version).

[deanjo]

The biggest issue I see with Linux 64-bit is that you can't choose between 32-bit and 64-bit libraries by default. That is, you only have one "/usr/lib" and in a 64-bit installation, they're all 64-bit libs. If you have a 32-bit program requiring a lib in /usr/lib, you're screwed.

Solaris for example requires both 32-bit and 64-bit binaries for drivers and libs to be installed together (i.e. the 64-bit version in under the "amd64" or "64" subdir and the system takes care of choosing the right version).

Not true, many linux distro's use a /usr/lib for 32 bit libs and /usr/lib64 for 64-bit.

[curaga]

Now, that is an annoying thing - even when you have a statically linked 32bit binary, if your system is 100% 64-bit (meaning 64-bit libs in /lib and /usr/lib), it won't run because it can't find a 32-bit /lib/ld-linux.so.2.

[npcomplete]

Not true, many linux distro's use a /usr/lib for 32 bit libs and /usr/lib64 for 64-bit.

really? I haven't checked out many distros at all but just going by mainstream ones like Ubuntu whos libs in /usr/lib are all 64bit and I recall Fedora was the same around FC8 or so last I checked.

[duby229]

really? I haven't checked out many distros at all but just going by mainstream ones like Ubuntu whos libs in /usr/lib are all 64bit and I recall Fedora was the same around FC8 or so last I checked.

Gentoo also has 64bit libs in /usr/lib, but they are symlinks from lib64. There also exists a /usr/lib32 which can be used for 32bit libs.