Benchmarks of Debian GNU/kFreeBSD vs. GNU/Linux

An anonymous reader writes "The Debian Squeeze release is going to be accompanied by a first-rate kFreeBSD port and now early benchmarks of this port have started coming out using daily install images. The Debian GNU/kFreeBSD project is marrying the FreeBSD kernel with a GNU userland and glibc while making most of the Debian repository packages available for kfreebsd-i386 and kfreebsd-amd64. The first Debian GNU/kFreeBSD benchmarks compare the performance of it to Debian GNU/Linux with the 2.6.30 kernel while the rest of the packages are the same. Results are shown for both i386 and x86_64 flavors. Debian GNU/kFreeBSD may be running well, but it has a lot of catching up to do in terms of speed against Linux."

Comments

Mod Article Flamebait

[TheRaven64]

Okay, so I only read the first couple of pages because it's Phoronix who have a history of inflamatory and misleading benchmarks, but from what I saw:

• Sometimes Linux is faster.
• Sometimes FreeBSD is faster.
• Usually the difference between the two is smaller than the difference between IA32 and x86-64.
• The tests were mostly either CPU- or I/O-bound, so there are lots of factors beyond the kernel that would affect the results.
• Debian kFreeBSD uses an old FreeBSD kernel, not sure how old the Linux kernel is but it's probably not representative of the speed of recent releases of either kernel.

Re:Holy moley !

[TheRaven64]

On most architectures, 64-bit code is slower. Pointers are bigger, which means you need more memory bandwidth to load them and you use more cache holding them. On x86-64, the situation is confused by the fact that 64-bit means 'using Long mode,' as well as 'using 64-bit pointers'.

Long mode gives you 64-bit registers (so you can store 64-bit values in a single register, rather than spread across two, doubling the number of 64-bit values you can store in registers), more registers, and a few other benefits like removing the 'must use EAX as the target' restriction on a lot of instructions (reducing the number of register-register moves, and decreasing instruction cache usage as a side effect). 64-bit pointers use more memory bandwidth and data cache.

For best performance on x86-64, you want pointers to remain 32 bits, but still run in Long mode. The OS should make sure that everything is mapped below the 4GB line for the process. As far as I am aware, no operating systems actually support this mode of operation. Without that, for any process using less than 4GB of address space, you have some advantages and some disadvantages when running in 64-bit mode. Whether the advantages outweigh the disadvantages, or vice versa, depends on the code.