Ubuntu 32-bit, 32-bit PAE, 64-bit Benchmarks

[Drago]

I also think that this huge difference is due to i486, rather than i686 optimization. Does anyone knows how 64-bit programs impact CPU on-die cache memory. Doesn't addresses in it, eat twice as much, than 32-bit code, effectively half usable cache size. How this affects smaller CPUs, like Athlon II for example?

[Dragoran]

The problems is they haven't specified this - in fact they've only told us the differences between the kernels

True....

Well I run one of the benchmarks on my system (c-ray .. one run with a 64bit binary; one with a 32bit binary).

Test system was a core i7 920 running at 3.8ghz with HT enabled (running 64bit kernel for both)
64 bit:

####################################
C-Ray:
Total Time

52.112 Seconds
52.261 Seconds
52.124 Seconds

Average: 52.16 Seconds
####################################

32 bit:

####################################
C-Ray:
Total Time

86.997 Seconds
86.774 Seconds
86.705 Seconds

Average: 86.82 Seconds
####################################

The numbers speak for themselves

[FireBurn]

The former, a 32bit app running on a x86_64 kernel cannot (and does not) provide performance gains like this (the kernel itself should have a very small impact if any (in most benchmarks); as shown with the PAE vs. NONPAE kernels).

The problems is they haven't specified this - in fact they've only told us the differences between the kernels

[Dragoran]

Have they proved that you should be using the Ubuntu 64bit CD or have they proved that if you use the 32bit CD you should install a 64bit kernel?

The former, a 32bit app running on a x86_64 kernel cannot (and does not) provide performance gains like this (the kernel itself should have a very small impact if any (in most benchmarks); as shown with the PAE vs. NONPAE kernels).

[FireBurn]

Well sse2 being part of the standard ABI is one of the advantages of x86_64 (i.e sse2 is always available).

And the summary gets it straight to the point there is NO reason not to use x86_64 on x86_64 capable hardware.

Have they proved that you should be using the Ubuntu 64bit CD or have they proved that if you use the 32bit CD you should install a 64bit kernel?

[Dragoran]

Did you just use a the 3 kernels and kept the same 32bit user space or did the 64 bit kernel use 64bit user space?

If the latter do you know what Ubuntu compiles it's 32bit user space as? If memory serves I think ubuntu are using i486 on 32bit user space where as the 64bit user space will be using sse2 as default which could explain some of the differences

Would it be possible to try the same test again using Gentoo or Arch (or another distro that uses i686 as default)

Cheers

Mike

Well sse2 being part of the standard ABI is one of the advantages of x86_64 (i.e sse2 is always available).

And the summary gets it straight to the point there is NO reason not to use x86_64 on x86_64 capable hardware.

[FireBurn]

Gentoo ? default ?
You may mean Sabayon (i586) ?
Once Ubuntu used to have i386, i586 and amd k8 binaries.
Just waste of resources (silicon). Gentoo is up to 4 times faster compared to Ubuntu. To gain such advantage in HW, you'll usually spend a lot of money.

What?

I'm trying to say that changing the default compiler options on 32bit systems can show huge differences

Phoronix could show the differences quite easily using their test suite

I think I've seen a non-Phoronix article showing just that using the PTS

[n0nsense]

Did you just use a the 3 kernels and kept the same 32bit user space or did the 64 bit kernel use 64bit user space?

If the latter do you know what Ubuntu compiles it's 32bit user space as? If memory serves I think ubuntu are using i486 on 32bit user space where as the 64bit user space will be using sse2 as default which could explain some of the differences

Would it be possible to try the same test again using Gentoo or Arch (or another distro that uses i686 as default)

Cheers

Mike

Gentoo ? default ?
You may mean Sabayon (i586) ?
Once Ubuntu used to have i386, i586 and amd k8 binaries.
Just waste of resources (silicon). Gentoo is up to 4 times faster compared to Ubuntu. To gain such advantage in HW, you'll usually spend a lot of money.

[xeros]

It's great to see such comparision!
I've put 3GB RAM into my machine few days ago and with default Ubuntu kernel I have only 2,5-2,7GB available. I was thinking to use PAE enabled kernel but I've heard about serious performance drop mentioned "everywere". I can't use 64bit kernel because my CPU is only 32bit.

[tettamanti]

One remark: in the switch from x86 to x86_64 the number of GPRs and XMM register is doubled, and of course 64bit ops require only one output register. In the OpenSSL (and John The Ripper) test case the big difference is probably due to the improved ISA rather than to bigger AS (iirc crypto was one of the showcases of earlier amd64 CPUs).
In general PAE will impact negatively the performance only once the kernel has to map/unmap pages that are not currently accessible; at least in OpenSSL, x264, blowfish and other CPU bound tests I don't expect a significant pressure on mm (hence the small difference between PAE and non-PAE).