3 ms·

I'm running several debian i386 virtual machines. I don't see a point running 64-bit os if the memory usage stays well below 3G. And last time I ran UnixBench o

by anemic 14y ago

I'm running several debian i386 virtual machines. I don't see a point running 64-bit os if the memory usage stays well below 3G. And last time I ran UnixBench on squeeze i386 was still faster than amd64. On bare metal it's a different story, though, but I still would think that there are more virtual servers than real ones.

zanny 14y ago
When you run 64 bit it assumes all the SSE extensions, the presence of the extra register sets, and everything between the 386 and 686 being available. It almost always performs better with software compiled to utilize the extra goods, even if it has slightly larger memory footprints.
- anemic 14y ago
  you're absolutely correct there. it might be that the performance difference I'm seeing is caused by the hypervisor or something else.
- Symmetry 14y ago
  Generally yes, you almost always see a performance increase with all the things x86-64 brings. But the increased cache pressure from 64-bit pointers is a real downside and the reason that pretty much every other architecture suffers in performance when it goes to 64 bits. If something about his workload makes it especially sensetive to cache pressure he could very well see a performance penalty, and I'd say heavy virtualization would actually make that more likely.
vegardx 14y ago
I'd say you waste time taking a conscious decision between 64-bit and 32-bit, there are few good reasons to not just go with 64-bit, and dwelling on it just wastes time. Do you have any metrics to support your claim that 32-bit Debian is faster than the exact same 64-bit distro? And what difference does virtual versus physical machines make? Heck, you can even run virtual 64-bit guests on a 32-bit host machine if the CPU supports either Intel-VT or AMD-V.
- anemic 14y ago
  I did find the results I got but without any further explanation they are not very useful: http://pastebin.com/WjiZNiSg http://pastebin.com/WjiZNiSg But interpreting those results indicates to me that there are possible problems with this platform where f.ex. file copy performance is ~50% faster on 32bit than 64bit. To me just assuming that there is no difference and go with instinct without anything concrete evidence is the wrong way to go.
- ciupicri 14y ago
  > And what difference does virtual versus physical machines make? As the OP seems to have suggested, virtual machines don't have a lot of memory.

by anemic 14y ago

zanny 14y ago

When you run 64 bit it assumes all the SSE extensions, the presence of the extra register sets, and everything between the 386 and 686 being available. It almost always performs better with software compiled to utilize the extra goods, even if it has slightly larger memory footprints.

anemic 14y ago
you're absolutely correct there. it might be that the performance difference I'm seeing is caused by the hypervisor or something else.
Symmetry 14y ago
Generally yes, you almost always see a performance increase with all the things x86-64 brings. But the increased cache pressure from 64-bit pointers is a real downside and the reason that pretty much every other architecture suffers in performance when it goes to 64 bits. If something about his workload makes it especially sensetive to cache pressure he could very well see a performance penalty, and I'd say heavy virtualization would actually make that more likely.

vegardx 14y ago

I'd say you waste time taking a conscious decision between 64-bit and 32-bit, there are few good reasons to not just go with 64-bit, and dwelling on it just wastes time. Do you have any metrics to support your claim that 32-bit Debian is faster than the exact same 64-bit distro? And what difference does virtual versus physical machines make? Heck, you can even run virtual 64-bit guests on a 32-bit host machine if the CPU supports either Intel-VT or AMD-V.

anemic 14y ago
I did find the results I got but without any further explanation they are not very useful: http://pastebin.com/WjiZNiSg http://pastebin.com/WjiZNiSg But interpreting those results indicates to me that there are possible problems with this platform where f.ex. file copy performance is ~50% faster on 32bit than 64bit. To me just assuming that there is no difference and go with instinct without anything concrete evidence is the wrong way to go.
ciupicri 14y ago
> And what difference does virtual versus physical machines make? As the OP seems to have suggested, virtual machines don't have a lot of memory.