More cores or faster CPU?

[davey]

My current ol' workhorse is about to bite the dust so I've been scouting for replacements. In a given price range the tradeoff on CPUs seems to be either more cores -- 1,2,3,4 -- or a higher clock rate. For Linux use, which is the better choice -- dual core running at 3.1GHz or quad core running at 2.5 for example? Does Linux make good use of multiple cores and will one or the other do better when our OS transitions to 64 bit? Will lack of multiple cores make the system obsolete sooner? I'm looking mainly at AMD CPUs like the Phenom II or Athlon II.

[Old-Polack]

davey:

I'd go for the most cores first, then the highest clock speed I could afford.

[Rudge]

I have a feeling that the answer may not be a simple one. I think performance will actually suffer for most general purpose software, if you choose a slower quad-core over a faster dual-core.

.02

Ref 1: http://www.codinghorror.com/blog/archives/000942.html
Ref 2: http://www.tomshardware.com/reviews/e8500-phenom-9350e,2010.html

[Rudge]

davey:

I'd go for the most cores first, then the highest clock speed I could afford.

If longevity is your goal, this is advice I would take.

[T6]

if you are in a budget, 3 cores at 2.8 sounds fantastic, i don't know if linux/kde uses more than one core in basic tasks

some apps can use more than one core but i never found this parameter in kde config

anyway, the idea of more cores and then more speed sounds very reasonable

the current trimester should bring the new amd and intel(possibly) 6 cores cpus so you should hold a little longer your decision

i heard something about 6 cores at 3.2ghz but still sounds very promising, this also will move the prices of 4 cores down drastically

i have read some comparisons of amd phenom II with very good results compared to the price it has

here are some comparisons(mostly win apps but can give you some idea of the performance)

http://www.tomshardware.com/charts/2009-desktop-cpu-charts/benchmarks,60.html

a reality in price/performance

http://www.tomshardware.com/charts/2009-desktop-cpu-charts/XviD-1.2.1,1383.html

and some prices in general

http://www.pricewatch.com/cpu/

[gilado]

2 cores will definitely give your system more responsiveness than one core. If you run any servers on this box then more cores always is better.

Most modern applications uses more than one thread of execution. Linux kenrel is an SMP (symmetrical multi-processor) which means that given multiple cores multiple thread will be distributed across the various cores for equal load.

Has it ever happen to you that firefox (running an applet or flash) or other application went into a tail spin consuming all CPU resources, bogging the machine to the point where you could not use the GUI to kill the offending application? Almost always that would just one thread spinning. On a multi core machine only one core would spinning with little effect on the overall usability of the machine.

This post is ancient, still provide answer to the basic questions
http://www.phy.duke.edu/~rgb/Beowulf/smp-faq/prive/mentre/smp-faq/smp-faq-3.html

Here's a more detail article from IBM
http://www.ibm.com/developerworks/library/l-linux-smp/
 

[YouCanToo]

FWIW, loudog bought a quad core to replace his dual core system and found out that his dual core actually out preformed his quad.  His dual core was faster in clock speed then his quad core was.  Perhaps you might drop him a PM and ask him for the nitty gritty details about his experiences. He also might see this post and respond.

[T6]

there is some logic  on that, if you are not going to do lots of multicore tasks a dual core with lots of mhz should be better but dual core cpus are in the extinction path, not even laptops are preserving dual cores, next generation of laptops is going to use 4 cores

[coonhunter]

My limited understanding is that the performance depends much more on whether the program code (that includes not only the application but also the OS with all its API libraries) has been optimised to run on a particular core architecture.If you're not planning to run mathematically intense applications(eg:video processing and such like) then go for a cheaper option.

[T6]

that applies for now, in a near future(next two years) all apps will use all cores available they can use

system reserves one core usually and leave others for apps(or at least windows does this)

[loudog]

 i do many many video and audio transcoding, extracting, pasting, mixing, video editing. i bought my first dual core platform to let me use virtualbox, web browse and transcoding etc. at the same time. it was an amd 3ghz with 1mb L2 per core, it was very fast compared to some of my other machines 1/3 faster doing side by side ripping transcoding tests. although i could run the vbox and transcode at the same time i could not say rip a dvd, transcode a full sized avi to psp (small screen mp4) and run the vbox at the same time. so i went for a quad. 2.3ghz 1mb L2, 2mb L3. disappointed much slower. could not run the vbox, transcode and rip at the same time. upon further investigation i discovered that some software, will use a seperate core for each instance running for example i could transcode 3 different files with one program opening a different instance for each file and it appeared the cpu's were being used seperately using gkrellem, but when i started say an instance of vbox it did not appear to get directed to its own core as the other running programs seemed to be but mixed into an already running one. another thing i noticed is that some software would use both cores but only a 50 50 type of split was happening for instance one extractor program would have core 0 at 78% and core 1 would be at 22% then quickly core 1 would be at say 43% and core 0 would drop respectivly to 57%. some software seemed to work much better with the multi core setup than others. so i would have to agree with coonhunter that it depends a lot on the software.

[davey]

Thanks for all the replies. A lot to think about. I don't foresee using Windows any time soon, so wonder if using Linux only changes the equation any. Do current OSes and apps support multiple cores significantly? Does that vary much between distros?

[T6]

linux kernel support multiple cores but as others said, no idea how the load is handle

specific apps can ask you if you have 1-4 cores and if you want to allow the use of multiple cores and how many cores

"Does that vary much between distros?"

each distro has tweaks and differences but in general all are the same so it depends mostly on the app itself unless you do specific changes before compiling