[mythtv-users] Gentoo 64bit and MythTV completely compatible?

Richard Freeman r-mythtv at thefreemanclan.net
Sun Jan 28 01:07:24 UTC 2007

Brian Wood wrote:
> On Jan 27, 2007, at 12:14 PM, Rod Smith wrote:
>> Although the speed benefits are small  
>> (about 5-20%
>> for most programs), x86_64 code can be a little faster than x86  
>> code on the
>> same CPU, all other things being equal.
> I think that, at least a couple of months ago, the consensus was that  
> there is nothing to be gained on a Myth system by running in 64-bit  
> mode.
> You have mentioned some of the reasons, code well optimized for 32- 
> bit, compilers not well optimized for 64-bit etc.

It definitely varies by application.  If the app can benefit from the
extra registers on amd64 it could have a significant speed boost.  I
think that compliers optimize for amd64 just fine in general, but of
course you won't get any hand-assembly that is 32-bit.  Many benchmarks
do run faster in 64-bit, but again it depends.

The larger data sizes can eat some RAM, and probably have an impact on
the cache as well.

I think a lot of the transcoding benchmarks being better in 32-bit go
back to the Athlon64 vs P4 days.  The Intel chips have always clocked
higher and for transcoding that can often give you better performance -
very linear processes that keep the pipeline full.  But, that was back
when 64 vs 32 was also an AMD vs Intel thing.  If you compared the same
processor working in both modes I don't think it was as clear-cut, and
of course today you can get 64-bit on either brand.

One thing I like about 64-bit is the seamless use of virtual memory
above 4GB.  I only have 2GB of RAM in this box, but I love to use tmpfs
drives and I can make them nice and big and just not think about it -
extra junk gets swapped out and it isn't any slower than just using a
straight hard drive.  That is harder to do if you have a 4GB ceiling on
virtual memory (although I think on linux there are ways around that).

It used to be that 64-bit was quite buggy, but now the only real issues
are 32-bit codecs and flash.  I don't care all that much about either,
and I can run 32-bit codecs in 32-bit if I have to.  Java used to be a
headache (buggy VMs), but that has gotten WAY better - comparable to x86
now.  And on gentoo a number of packages are now maintained primarily on
amd64 and x86 follows.

At this point as long as you don't have any major blockers I'd probably
just go with amd64.

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