x86_64 as Fedora's primary platform

[Gregory Maxwell]

On Mon, Sep 27, 2010 at 1:58 PM, Stephen John Smoogen <smooge at gmail.com> wrote:
> On Mon, Sep 27, 2010 at 13:48, Gregory Maxwell <gmaxwell at gmail.com> wrote:
>> The Fedora web resources (e.g. http://fedoraproject.org/get-fedora )
>> continue to promote i686 installs over x86_64, the result being that
>> only a third of fedora users are on x86_64.
>>
>> When will the Fedora project begin recommending x86_64 as the
>> preferred option on the relevant hardware?
>
> Well while many people have x86_64 capable hardware, 66% of the
> systems have less than 2GB of ram installed on them. The gain of extra
> registers is taken over by the amount of extra memory used. So I am
> not sure pushing 64 bit will gain much beyond "why am I using so much
> memory now?" messages.

I agree that systems which are very short on memory will be happier
with i386 but I don't think 2GBytes is at all a reasonable cut-off.
None of the x86_64 desktops I have access to are currently using more
than 1Gbyte (ignoring cache, of course).  Only something like 11% of
systems have less than 512MBytes, roughly 1/3rd with less than 1Gbyte.

If you're not swapping x86_64 bringing increased performance is easily
demonstrated, and has been previously demonstrated here... if there is
any doubt on this point I'd be glad to run some more benchmarks to
demonstrate it.

E.g. On a random 720p video file (http://xiph.org/video/vid1.shtml)
Theora decode is over 20% faster with x86_64 compared to i686 on the
same hardware (X3360), even though libtheora can detect and use SSE2
at runtime. I admit that this is probably one of the bigger
differences— the point is that the improvement is can be very
non-trivial on CPU bound code that actually matters to users.


On Mon, Sep 27, 2010 at 1:53 PM, seth vidal <skvidal at fedoraproject.org> wrote:
> i686 will run on x86_64 and i686 machines and on the overwhelming
> majority of hw someone will happen to have.
>
> x86_64 will not.
>
> until i686 is uncommon (which is still not yet) I think we should keep
> the default i686.

I find it somewhat incomprehensible that Fedora has chosen to
_completely exclude_ pre-P6 cpus and came fairly close to also
excluding x86 systems without SSE2 (which are still being mass
produced)—  but Fedora won't promote x86_64 as a leading option when
it only constitutes a majority of the target system.

What is the thinking here?  Is it really better to make Fedora not run
at all on part of the installed base in order to force-fit the i686
builds as high performance options, simply because defaulting to the
real high performance option will make the install process a little
trickier for users on netbooks?


On Mon, Sep 27, 2010 at 1:59 PM, Athmane Madjoudj <athmanem at gmail.com> wrote:
> Most (if not all) Atom-based netbook are i686.

Indeed, the netbooks have special requirements.  The in-order atom
CPUs alone benefit from fairly different compiler scheduling which is
less than ideal for the extensively out of order cpus used everywhere
else.

The netbooks are also special in a number of other ways... I doubt
there are many desktops out there with 1024x600 screens.

Since the needs of netbook users are so specialized, why aren't they
being directed to a netbook specific spin?