Ubuntu 16.04 LTS 32-bit vs. 64-bit Linux Performance

[Nille]

Where does the performance gain come from?

AMD64 is not only more Memory. The same for AArch64. This ARM CPUs can more as only Address more Memory.

Delgarde unfortunately x32 is not used in the wild and the performance gain is to small for the work.

[jacob]

AMD64 specified more registers and function parameter passing using those, so basically less memory references which can stall
Floating point can also assume SSE2 at least, rather than the old 387 style FP unit compatible 80bit floats.

Code which has lots of pointers may run slower, especially if it exceeds L1 cache, because of the doubling of memory address sizes.

Another important factor is that amd64 has new and much better addressing modes, including a real IP-relative mode. Since on Linux, all shared libs are required to be position independent, in old x86 they must emulate relative addressing by calculating addresses manually. Not only it slows the code down by itself, it also adds to the already high register pressure. 64bit code doesn't suffer from this problem.

[Delgarde]

Delgarde unfortunately x32 is not used in the wild and the performance gain is to small for the work.

Pretty much, yeah. It's just easier to build everything 64-bit whether it needs it or not, than to ship a distro with two versions of all the common libraries, and for someone to make a call on whether any given application should be la 32-bit or 64-bit version. Dual 32/64-bit architectures are just a pain in the neck to deal with...

And yeah, in the benchmarks I've seen, the benefits are negligible... no significant performance gains, and while the memory savings can be more substantial, they don't make up for the disadvantages unless you're running a very constrained system already.

[Passso]

That's kind of like asking why a shovel picks up more sand than a spoon.

That's fun, because a couple of years ago spoons were in general picking up more sand than shovels...

[Hammond]

One reason to run Linux 32 is to avoid 32 bit libs when running Steam games (native or with Wine). And I'm not sure Blizzard has made WoW 100% 64 bit yet.

[Tomin]

One reason to run Linux 32 is to avoid 32 bit libs when running Steam games (native or with Wine).

On 32 bit you'll use 32 bit libraries anyway, but there aren't additional 64 bit copies. I guess you meant something like that.

And I'm not sure Blizzard has made WoW 100% 64 bit yet.

See the link.

[Hammond]

On 32 bit you'll use 32 bit libraries anyway, but there aren't additional 64 bit copies. I guess you meant something like that.

Yes I ment when I play 32 bit games on 32 bit Linux, I don't need any extra 32 bit libraries (obviously :-)).

See the link.

With WoW in the same sentence as Blizzard, and you didn't refer to World of Warcraft? :-)
(I was thinking if I needed 64 bit libraries or not).

[Tomin]

With WoW in the same sentence as Blizzard, and you didn't refer to World of Warcraft? :-)
(I was thinking if I needed 64 bit libraries or not).

That was just somewhat funny coincidence to me.