x86_64 mail servers

Mailscanner mailscanner at mckerrs.net
Thu Feb 9 11:28:05 GMT 2006

Mark Nienberg wrote:

> Matt Kettler wrote:
>> Mark Nienberg wrote:
>>> I've seen comments on this list that the x86_64 didn't seem to make
>>> much
>>> difference and I admit it is simpler to use the plain x86 version, but
>>> it bothers me a little to intentionally not use the software that is
>>> specifically configured for the chip.
>> Why does it bother you?
>> Theoretically x86-64 should be slightly slower for most uses unless you:
>> 1) have a process that needs > 4gb of virtual address space
>>     -or-
>> 2) does a lot of 64 bit math that can't be performed with SSE
>> The ability to have huge processes and large amounts of physical ram
>> is the
>> primary benefit of using a 64 bit computing architecture. The
>> drawback is that
>> pointers become larger, taking up more memory, and causing more
>> memory I/O than
>> would be needed if the app was 32bit. Unless you're actually using
>> the larger
>> memory space you're increasing overhead without any benefit
>> whatsoever. Very few
>> apps have such large memory footprints outside the realm of scientific
>> simulation or massive database crunching.
>> The other benefit of a 64bit computing architecture is the ability to
>> do 64 bit
>> math operations in one instruction instead of a series of 32 bit
>> operations.
>> However, very few applications regularly have any use for 64 bit
>> operations
>> outside of crypto, some games, and high-end engineering/physics. Even
>> these
>> regularly get their needs filled by using SSE, so the 64-bit math
>> benefit is
>> very limited.
>> There's some benefit here to apps using 64-bit file offsets or 64 bit
>> time
>> format, but I've never seen a "regular" application where either kind of
>> calculation was performed often enough to have a noticeable impact on
>> performance. Some scientific simulations may do a lot of 64bit time
>> calculations, but most of those could readily use SSE for it.
> So I can take the easy way out and not feel guilty about it?  Fantastic!
> Thanks for your explanation.
> Mark Nienberg

One thing that the i386 version will do it disable AMD's cool 'n quiet.
It appears only to work when you run in 64bit mode. My server runs in my
garage so heat  (or lack thereof) is more imporant to me than a
'slightly' slower machine.

Has anyone quantified 'slightly' ?


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