[gentoo-amd64] Re: Is there any difference with 4 core?

[Duncan]

"P.V.Anthony" <pvantony@×××××××××××.sg> posted
46B0A3D5.6080203@×××××××××××.sg, excerpted below, on  Wed, 01 Aug 2007
23:16:37 +0800:

> Now the question is, is it better to go with 2 core or 4 core?
>
> The reason for this question is, that I heard there is a diminishing
> return with more cores. Not sure if this is true with kernel 2.6.21 and
> running at 64bit.
>
> The server needed to built is for the following apps.
>
> Hardware.
> 1. Tyan Tank GT20 (B5191)
> 2. 2 x Sata drives
> 3. Software raid 1
> 4. 4Gb ram ecc
> 5. Intel Core2Duo E6420 or Intel Core2Quad E6600
>
> Apps.
> 1. Gentoo linux 64bit
> 2. Apache 2
> 3. MySql
> 4. Postgres
> 5. Qmail
> 6. Pure-ftpd
> 7. Mod_perl
> 8. php
> 9. ruby
>
> Will all the instances of the apps be shared among the cores?
>
> Please share the comments.
>
> I would really like to save some money. If the 2 core can do the job
> there is quite a bit of savings buying just the 2 core.

Your application is server, and others have dealt with it.  I'll answer 
for desktop/workstation use, however, since that's what I'm doing here, 
and other readers may be interested.

I've been running a dual socket Opteron for some time now, originally 
with Opteron 242s.  I've upgraded memory to 8 gig (2x2 gig for dual 
channel off of each CPU/memory-controller, NUMA so each CPU tries to 
localize memory access to its own 4 gig), and run a 4 spindle kernel RAID 
(1, 6, 0).  /tmp (with /var/tmp a symlink to it) is on tmpfs, so making 
use of some of that 8 gigs of RAM.  RAID-1 /boot, RAID-6 main system, 
RAID-0 striped for speed swap (4x4GB=16GB swap), ccache, $PORTDIR, and 
/usr/src.  Thus, there's little needing upgrade on the general system.

This was my first dual CPU system (before dual-cores came out), and I 
really appreciate the flexibility it gives me.  That said, now that I'm 
used to it, the dual CPU (single cores) is definitely a bottleneck at 
times, and I could really use a quad system.  That in fact is what I'm 
planning.  I've money set aside for upgrading to dual dual-cores, maxing 
out the system with Opteron 290s, but at a going price of $1400+ for the 
pair on pricewatch.com, I'm hoping to wait until Barton comes out and 
that it will lower the price on the old socket 940 Opterons.  I'm hoping 
it'll drop the pricepoint to about the current one of the 285s, saving me 
$300-400.

I'm definitely looking forward to the upgrade, tho.  It's nice to be able 
to run two CPU hogs, CPU affinity set so each is scheduling on its own 
CPU, without seriously affecting responsiveness.  However, the two CPUs 
is definitely a limiting factor, now, particularly since other than 
memory, the rest of the system's all attached to socket 0, so apps such 
as X run more efficiently on it.  By upgrading to dual dual-cores, I'll 
have two cores able to schedule on that direct-connected socket 0, plus 
two cores on the less well connected socket 1.  Where now I can run X on 
CPU 0 and my other CPU hogging app on CPU 1, I'm quite looking forward to 
being able to run both on separate cores on socket 0, while the two cores 
on socket one could be doing a full emerge -e world for example, without 
affecting my CPU intensive interactive stuff on the two socket 0 cores 
/at/ /all/. 

So yes, I appreciate the dual CPU, but while the popular press is still 
asking if desktop tasks can scale to dual-core, let alone quad-core, I'm 
on dual-CPU right now and definitely could use the quad-core or 2 by dual-
core system right now!  I can't at this point say that I'd be able to 
make good use of 8 cores, but four, certainly, as two is feeling a bit 
constrained at this point.

As for Intel vs. AMD, with the hypertransport interconnect system AMD 
has, with AMD's hardware IOMMU for DMA access above the 4 gig boundary 
(Intel has to emulate it with software bounce-buffers on most of its 
hardware, kinda nullifying the point of DMA), and with the vaunted Intel 
performance lead mostly a 32-bit phenomenon, dual dual-core AMD is often 
more efficient on 64-bit than quad-core Intel.

The biggest down side for AMD here is the severe lack of open source 
support for anything faintly modern, GPU-wise.  Unfortunately, Intel's 
the only real option for anything even half modern in terms of open 
source driven graphics chipsets.  For an x86_64 Linux desktop/
workstation, that more than cancels out the lead AMD would arguably have 
in multi-core/multi-CPU support, and if I were buying now, it'd be Intel 
for that reason.  AMD simply has to get its act together, and release at 
least enough specs for its ATI graphics product so the community can 
build the drivers itself.  Or sponsor its own open source drivers.  
Either way.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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