x86-64 on i386 (was Re: Promoting i386 version over x86_64?)
Paul Jakma
paul at dishone.st
Sun Dec 13 22:24:29 UTC 2009
On Sun, 13 Dec 2009, Chris Adams wrote:
> As soon as you bring in even one 64 bit user-space program that is run
> much, you've pulled in at least glibc and friends. At that point, you
> might as well run all (or as close to all as possible) 64 bit
> user-space, because the libraries are shared (code will be in the cache,
> etc.).
That's assuming that the footprint of libraries relative to distinct
applications is large enough to cancel out the space savings. (I have
no data either way). A 64bit kernel doesn't need any 32bit userspace.
An X server, on my 32bit system has about 8.5MB of programme text
(server and libs) and loads about another 1.5MB worth of modules
itself, i.e. 10MB.
So if you ran a 32bit system with a 64bit kernel and X server, you'd
lose out on about 10MB of shareable code. For comparison, my 32bit
system has O(10) times that allocated to things like browsers and
feed-readers. It's using 4.8GB in total (ex buffers/cache)
apparently.
Space for text (programmes, code) is simply insignificant these days,
compared to the huge amounts of data which programmes allocate - data
which sometimes includes a lot of pointers.
You're also assuming that this cancels out the other benefits.
> The only time my systems have run 32 bit code in several years is for
> the Flash plugin (since the open-source plugins don't seem to be able to
> keep up and since the 64 bit Adobe plugin doesn't seem to get the
> security updates) and sometimes the Acrobat Reader plugin (since I've
> run into websites that assume they can embed PDFs in the page and AFAIK
> there's no plugin for Evince).
It's interesting that both you and drago have "almost always" (to
paraphrase) run 64bit pure systems. Surely that *reinforces* my point
about the futility of "64bit pure systems" as an achievable goal (in
the aggregate across all reasonable uses of a distro), and i386 being
a de-facto standard for software interfaces.
> As for the RAM overhead of 64 bit code vs. 32 bit code, I don't see it
> much in the real world. I have one 32 bit desktop at work, and
> comparing the resident RAM usage between it and a 64 bit desktop, I
> don't see much difference in the common desktop programs.
That's the wrong comparison - compare the aggregate RAM usage, with
each system in similar states.
> I know that for some reason PHP on 64 bit arches bloats up
> significantly (at least older versions), but that's the only major
> difference I've seen.
Pointer rich data structures, likely..
Anyway, as I don't intend to contribute anything, I'll try stop
making noise.
Aside to the list: Thanks for all the hard-work on Fedora ;)
regards,
--
Paul Jakma paul at jakma.org Key ID: 64A2FF6A
Fortune:
Dogs just don't seem to be able to tell the difference between important people
and the rest of us.
More information about the fedora-devel-list
mailing list