Re: Does my processor support 64bit kernel?

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Tue, 11 Feb 2014 23:13:23 +0530
    From:        Mayuresh <mayuresh%acm.org@localhost>
    Message-ID:  <20140211174323.GA1997%SDF.ORG@localhost>

You probably have all the answers you want already, but ...

  | I am using NetBSD i386 on my desktop.

In that case ... (provided the NetBSD you have is modern enough)

        cpuctl identify 0 | grep EM64T

(since you know it is an Intel processor already, if it was an AMD
processor that would need modifying).  If a line containing EM64T is
output, you have a processor that can run 64 bit if you want it to
(which doesn't necessarily mean that you should - it all depends upon
how much RAM you have (and want, and can fit in the motherboard) and
what kind of applications you run.

  | dmesg describes the processor as follows:
  | 
  | cpu0 at mainbus0 apid 0: Intel(R) Pentium(R) D CPU 3.00GHz, id 0xf65
  | cpu1 at mainbus0 apid 1: Intel(R) Pentium(R) D CPU 3.00GHz, id 0xf65

Note that could be dual core, or it might be (really) a single core CPU
with hyperthreading enabled.

  | 1. Is there any way (either some system information command or
  | manufacturer web page) that can confirm whether above is a 64 bit
  | processor or not?

cpuctl identify N  (all the cpus will be 64 bit, or not, so you can
check any one of them, no point checking both).    If your NetBSD is
too old, look at the info it prints early in the boot sequence (from
/var/run/dmesg.boot) - old NetBSD's (before cpuctl was added) used to
print the CPU info as part of the boot sequence.

If you found the correct Intel web page, it would probably say as well,
and so would the processor box, if you still have that (if you ever had
that.)   But cpuctl is much easier than hunting for either of those!

  | 2. Which sets shall I use for an Intel 64 bit processor - amd64?

Yes.

  | A bit worried since wikipedia page below says there are differences between
  | amd64 and intel 64

Yes, but (almost) no-one has ever seen a processor using the
Intel 64 bit architecture (IA-64) so you can ignore that.

Intel support AMD's 64 bit design (AMD got to market first - by a long way)
and that's all that really exists now.

  | 3. Is there any perceivable performance gain on a 64 bit processor, with
  | 64 bit system as against 32 bit system? (I'd like to give it a try
  | irrespective of that, though just thought of asking.)

There can be, when dealing with 64 bit (or bigger) data, there will be
fewer references, fewer instructions, also amd64 has more registers, so better
optimisation is possible, ...   There can also be performance losses
(everything is bigger, uses more ram, can lead to more paging...) and
simple stuff needs more bytes (referencing any pointer) so uses more cache
space, leading to lower effective cache utilisation.

Whether any of this is perceivable, as opposed to "there, but for practical
purposes unmeasurable" entirely depends upon other stuff in your system (using
more ram doesn't really matter if you have plenty free, using a bit less cpu
time doesn't really help if most of the time is spent in the idle loop...)

kre