[tlug] 64- vs. 32-bit Linux Installs

[Curt Sampson <cjs@example.com>]

On 2016-04-24 13:18 +0100 (Sun), Darren Cook wrote:

> Branching off-topic, is "low-spec" a reason to not use 64-bit? The first
> page I looked at [1] suggests to only install the 32-bit version if your
> CPU is 32-bit (lscpu lists only "32-bit" under CPU op-mode).

Well, you definitely don't want to get stuck having to re-install if you
put more memory in your computer.

> Ah, the last comment on that page says if only 3GB of RAM then the
> 64-bit version was more sluggish, at least as of Ubuntu 13.04. (But if
> true, I'm still curious as to why.)

All your 'int' values become 64-bit instead of 32-bit and, while this
can speed up certain CPU-intensive operations, most daily operations
that look CPU-intensive are actually memory-bandwidth-intensive, and
talking to the DRAM (rather than pulling values from one of the on-CPU
caches or, better yet, manipulating only data in registers) is about the
slowest thing your computer can do, short of I/O.

So basically, in a 64-bit system you may well at certain points be
transferring nearly twice as much data between RAM and cache, which
may slow you down a bit. (Or may not even be noticable.)

And, of course, since you're using a bit more memory, you may also drive
yourself into paging to disk, depending on what you're doing, which will
utterly destroy performance.

But honestly, for everyday applications it's extremely difficult, if not
impossible, to determine in advance how bad the performance hit will be.

cjs
-- 
Curt Sampson         <cjs@example.com>         +81 90 7737 2974

To iterate is human, to recurse divine.
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