[nylug-talk] LOWMEM vs. HIGHMEM performance advantage?

[Bryan J Smith]

6rom: Alex Pilosov <alex at pilosoft.com>
> (i will call it x64 and spare me)

Oh, I just caught this. It 100% explains your view.

*NEVER* call it Linux x86-64/AMD64 or Linux IA-32e/EM64T as x64.
X64 is the *WINDOWS* name for a product with a Long Mode kernel with almost enitrely Win32 libraries.
Linux ships native, Long Mode libraries and binaries, x64 (Windows) largely does not.

X64 exists because the Win32 API has been extemely difficult for Microsoft to port to x86-64/IA-32e.
Windows for Alpha was always 32-bit, never 64-bit, because of Win32.
Even the "test" versions of Alpha Win64 suffered the same non-sense of WoW.

This is utterly unlike GNU/Linux that has been almost entirely 64-bit clean for.a long, long time.
Only.a few system-level details we're issues back in 2.2 and earlier, as well as legacy codebases (largely pre-POSIX 2001).

> in empirical tests, bloat is anywhere between 25% to 50% depending on application.

Static code/data bloat is dependent far more on data alignment, not memory model.

As far as 25-50% slower, yes, x64 apps on x64 OSes are 25-50% slower than x86 apps on x86 OSes.
In fact, x86 apps are faster tjhan x64 apps on x64 OSes. Why?

Because x64 uses WoW (Windows on Windows) so one memory model can call the libarary of another.
This is largely Win64 calling Win32, utterly destroying native speed execution.
It 0% applies to Linux, and your use of x64 here should have been my "wake up" call.

Linux distros either ship either all Long Mode libaries (possibly with a change root), or the POSIX-standard /lib64 or native, /lib for compatibility.
Of course running two apps, one Long Mode one x86, that call the same library will result in two different libraries being loaded (with associated, added memory usage).

But I've yet to see any argument made about the "bloat" of x86-64 outside of library redunancy or stupid things other OSes do, like Windows x64.

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Bryan J Smith - mailto:b.j.smith at ieee.org  
http://thebs413.blogspot.com  
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