I once heard that Linux does not balance the loads on 2 processors to well, and that the extra processor would basically just be sitting there idle most of the time.

Does anyone here have experience with adding an extra processor to their Linux box? If so how did it perform after that? What were your experience etc.

Thank
John

Hmm I'm interested to know too, I have a linux box with 2 processors too.

thats untrue, linux will balance the load with dual cpu's ..you need an SMP kernel, check your install media to see if there is an SMP RPM there! There should be one, on Mandrake 8.1, it is called kernel-smp-2.4.8-26mdk.i586.rpm and can be found on the first CD. The only difference between different versions of Mandrake should be the version number of the RPM.

rpm -Uvh /mnt/cdrom/kernel-smp-2.4.8-26mdk.i586.rpm
(correcting the file name as apropriate)

If not you could be looking at recompiling your kernel. If it comes to that try this link

http://www.linuxdoc.org/HOWTO/

2 processors definately make a difference. The majority of our servers are dual P3 Tualatins and they fly - they'll outperform any single P4 configuration.

Thanks for you valuable input! :)

John

Yes, our newest server is a dual p3 talutins and they perform fast then we need them to!

Dual P3s kick ass, especially Tualatin-class ones. Even my three Dual P3 850Mhz machines I recently picked up as a deal from ThePlanet outperform my P4 machines there.

Whoever told you that the second processor was useless is on crack. It deffinately makes a difference.

Aaron

Wow really? dual 850mhz is better than a p4 2.0-2.4 ghz ???

Originally posted by DarktidesNET
Wow really? dual 850mhz is better than a p4 2.0-2.4 ghz ???

just get some dual P4 xeons ..... I think it's about CAD 470 / cpu for a P4 xeon 2.4Ghz... add $500 for a good mainboard... and that's a nice machine! :)

Not in my budget but I would like to have one. ;-)

Generalizations are dangerous, however as most people stated, a dual processor system will perform better.

Make sure that:

1.- You run the SMP kernel
2.- Your motherboard is good
3.- Your CPUs are actually being used

For those with the budget a system with hyperthreading might be the best value.

On dual systems I have been able to run about 1200 processes (low CPU intensity) fairly well. I have never achieved that on a single CPU system.

Alberto Alonso

Originally posted by a_alonso
hyperthreading might be the best value.


hyperthreading is 50% marketing, 40% b.s. , 10% actual performance...

just my opinion.

My dad always told me:
Opinions are like a$$holes - everyone has one and they all stink except your own. Then once in awhile yours blows in your face and you realize it stinks too!

Couldn't resist ;)

Originally posted by dhabets


hyperthreading is 50% marketing, 40% b.s. , 10% actual performance...

just my opinion.

Your right - hyperthreading is just a technical term intel used describing the ability to use a dual Pentium System. Standard Pentium 4's are not capable of working on a dual motherboard system. Hence Intel must compete with AMD and they make their 3.06Ghz "Hyperthreaded" chip - its all hype.

I have dome some testing on database servers with dual CPUs + hyperthreading, for a total of 4 CPU visible.

The results can be summarize as follows "The system hardly broke a swet"

However, it did seem to relax more when hyperthreading was enabled.

If your app is good working in parallel processing, and the botleneck is CPU, then hyperthreading probably helps. If the botleneck is anything other than the CPU then it is not going to make a difference.

Most of what I've seen on the Linux kernel lists indicates the max perf. increase around the 30% mark.

Again, it all depends on your specific app.

I beg to differ on the hyper-threading issue, it does make a difference, you just need to read the following: http://www.anandtech.com/IT/showdoc.html?i=1747 to see that i makes a difference in the real world.

Originally posted by Hostkookster


Your right - hyperthreading is just a technical term intel used describing the ability to use a dual Pentium System. Standard Pentium 4's are not capable of working on a dual motherboard system. Hence Intel must compete with AMD and they make
their 3.06Ghz "Hyperthreaded" chip - its all hype.

Not quite correct.... reference http://www.intel.com/ebusiness/hyperthreading/index.htm?iid=ebus+home_ne_1&

What is Hyper-Threading Technology?
Faster clock speeds are an important way to deliver more computing power, and Intel has led the way with industry-leading processor frequency. But clock speed is only half the story. The other route to higher performance is to accomplish more work on each clock cycle, and that's where Hyper-Threading Technology comes in. Hyper-Threading Technology enables the processor to utilize its execution resources more efficiently, delivering performance increases and improving user productivity.

Benefits of Hyper-Threading Technology-Enabled Systems Include:

Increased system responsiveness in multitasking environments, allowing users to do more in less time.
Increased performance for both current and future multithreaded applications that take advantage of Hyper-Threading Technology.
Enhanced value to users by increasing headroom to handle peak workloads.
Flexibility for IT to run critical background applications for a more secure, reliable, and manageable computing infrastructure, without interrupting user performance or productivity.



And we can debate about what benefit (or lack thereof) it will give, but it's much like the mmx extensions debate... Right now hyper-threading won't do sh*t for me...

Originally posted by KDAWebServices
I beg to differ on the hyper-threading issue, it does make a difference, you just need to read the following: http://www.anandtech.com/IT/showdoc.html?i=1747 to see that i makes a difference in the real world.

From the conclusions on Anandtech:

"While unable to replace the power of additional CPUs, Hyper-Threading provides no less than a 30% boost in I/O loaded situations, which occurs quite often in reality. In fact, once you factor in the latency introduced by traffic flowing over the network before getting to the server there are quite a few opportunities for Hyper-Threading to fill those moments of idle execution. "

"However, for lightly loaded servers that don't experience much I/O utilization there may actually be a small performance drop if Hyper-Threading is enabled. In any situation where CPU performance is a key issue, enabling Hyper-Threading does seem to provide a performance gain. We can attribute this to an updated revision of the Hyper-Threading architecture in the new Xeons as well as the faster clock speeds that these processors are running at."

"Needless to say, that if developers can come even remotely close to implementing this sort of thread level parallelism in desktop applications then Hyper- Threading will bring the Pentium 4 much more success than any other single architectural improvement."

I'd say make up your own mind based on that....

Originally posted by Rob_AcuNett
Yes, our newest server is a dual p3 talutins and they perform fast then we need them to!

Is the Tualatin the one w/ 512k cache?

Tualatins usually come with 512k cache, although I believe they did do some with only 256k cache.

In a server environment Hyper-threading is beneficial (unless you don't put any load on them of course) but for your desktop PC it's not going to make any difference really.

Thanks for the anandtech link I didn't see that while I was researching.

As for the desktop I don't think that hyperthreading will be worth much in there, as most desktop users are single tasking.

However more and more server apps are capable of parallelizing themselves well. Web servers, databases, email servers, monitoring servers, etc. All of these do benefit from hyperthreading.

The only problem now is getting enough customers per box so that the CPUs actually swet :-)

There's also an interesting look at Hyper-threading at 2CPU (http://www.2cpu.com)
I find it frustrating how the real server class Intel configurations have become so expensive. The dual P3 used to work pretty well, but now that they're older the prices are climbing and they are more and more scarce. The Tuallies are great, but very pricey as well. Xeons? Arrgghh! I took my first dive into dual Xeons this week. After $220 on the mobo, $250 on CPUs and $300 on memory I have no recollection as to why I thought this was a good idea. Maybe the Tualatins aren't so bad afterall!

no question Linux does make good use of multi processer unless the guy is an *** to use the normal kernel:cool:

Yep, Linux is getting better about this.

The other big thing is the scheduler and having over 1000 processes, but that should be a completely different discussion :stickout:

I have a Dual CPU 1GHZ P3 that work great. I just finished building a DUAL CPU XP1800+ and overclocked it to 2000+MP Speeds. And wait before you techs say XP does not work in dual config. The chips were modified to accomplish this. I was thinking of running LINUX on it I am running XP Pro right now.

The modified XPs aren't as stable as real MPs and I wouldn't recommend that for use in a server.

I have dual AMD Athlon MP 1800's

Works like a charm :cool:

So P4 3ghz doesn't work in dual mode? Or did I misread what someone mentioned.

Lastly is the SMP kernel all you need to make use of the hyper threading in P4 3ghz?

My understanding is no and no.

No SMP with the current P4's. Want duals, you need to go Xeon.

You need Windows XP or a 2.4.x Linux kernel - at least as I recall of the Intel presentation.

There are numerous articles on the benefits (or lack thereof) of HT. As usual, it depends.

If you get a P4 with hyperthreading it will work in dual mode. Any P4's produced without hyperthreading technology do not work in dual mode.

so are you saying that P4 will work in dual mode as a single processor or that it can have dual CPUs as long as it has hyperthreading technology?

The P4 is not SMP. With HT it will appear as two CPUs, but you can only run one physical CPU.

Potsie
No, you can run 2 P4 CPU's with hyperthreading. That was one of the main features - to have 2 CPU's running on 1 mobo. They didn't do it for their regular P4's and got burned by AMD. Their chips supported a dual chip mobo. There might not be a mobo that supports 2 P4 HT right now but the technology in the chips allows it.

Hey, a very related article on hyperthreading and linux:

http://www-106.ibm.com/developerworks/linux/library/l-htl/?ca=dgr-lnxw01HyperThread

It seems that with the 2.5 series the improvements have gone from upto 30% to upto 51% performance improvement.

Originally posted by Hostkookster
Potsie
No, you can run 2 P4 CPU's with hyperthreading. That was one of the main features - to have 2 CPU's running on 1 mobo.
Wow.. that's news to me. It's about time. Now hopefully the prices will come down from the stratosphere to make them affordable as a server platform. There wasn't any good mid-tier solution lately. It was dual P3s or dual Xeons (if you're an Intel server guy - which was getting harder to justify).

It's not the Xeon chips right now that are so pricey though - it's the motherboards which support dual xeons.

I agree about the xeon chips not being that pricy.  A Tualatin 1.4 is the same price as a Xeon 2.0 at a few major online vendors.  A decent dual Tualatin MB can be had for $150, while the Xeon board is close to $500.  Those dual channel Ultra320 on board controllers really drive the price up.

I have a redhat server with 2 processors, and it runs fantastic. Runs a game server, two ircds (one with fairly high traffic), among other things, and it barely has a load on it. It is definitly noticeble and worth the extra couple bucks. If it wasn't, why would they offer it? It could be your OS or configuration that causes it to not be as effective as desired.

You can run dual HT cpu's .. will look like 4 cpu's to the OS...

What kiook was saying is simply not fully true

I have read numerous places that there is NOT and will NOT ever be a dual P4 board, chipset, or whatever.

What would the point of a XEON be then?

I highly doubt Intel would allow this. I think Potsie summed it up best.

i agree with potsie and innova, there isnt, and wont be any dual p4 motherboards... p4's are not capable of being run in smp... all hythreading does is give you two virtual cpu's... its nothing but marketing.

Would it balance 4 XEONS OK?