FAQ: Dual Core

[mpasternak]

I have no problem with it in your guide or what not.

I don't care about credit or anything

I've been lurking and not posting a lot for a while now because i'm just getting bored and sick of the same question over and over and over and over and over again

i wish people would just read other threads or do a search before asking

 

[RichPLS]

Take credit where it is due dude. Specially good credit.

 

[Ned_Flanders]

I'll take credit then.

Thanks guys.

 

[DRAGoNX]

Sticky FTW!!

I still find people asking about wether 2.4+2.4=4.8

Just make it a sticky so all I have to do is flame those people for NOT READING A STICKY.

 

[TimidKiller]

4. Seems to good to be true, What’s the Downside?
A> while they handle multiple threads well, Single threaded applications will still only use 1 core / 1 CPU at a time, Leaving the 2nd CPU core often underused or not used at all. Games in particular are virtually all single threaded. (We’ll call thread A)
CPU1:AAAAAAAA
CPU2:BCDBCDBCDBCDBCDBCDBCDBCD
What ya can see that if you set the game to use up an entire Core, yes, you can run other threads on the 2nd core without a hit to the game performance. BUT those background threads will all have to share the 2nd core and will take a bit longer to run. to further this problem. The OS doesn’t fully optimize the CPU's this way. and there are some intermittent threads that make it onto Core 1.
CPU1: AABCABDAAAACDA
CPU2: BCDBCDBCDBCDBCDBCD
The game is still slowed down even more by the other CPU intensive applications.

8O :?: Confused me a bit here... Isn't this:
CPU1: AABCABDAAAACDA
CPU2: BCDBCDBCDBCDBCDBCD

better than trying to run AABCABDAAAACDA AND BCDBCDBCDBCDBCDBCD on just 1 CPU?

 

[DRAGoNX]

4. Seems to good to be true, What’s the Downside?
A> while they handle multiple threads well, Single threaded applications will still only use 1 core / 1 CPU at a time, Leaving the 2nd CPU core often underused or not used at all. Games in particular are virtually all single threaded. (We’ll call thread A)
CPU1:AAAAAAAA
CPU2:BCDBCDBCDBCDBCDBCDBCDBCD
What ya can see that if you set the game to use up an entire Core, yes, you can run other threads on the 2nd core without a hit to the game performance. BUT those background threads will all have to share the 2nd core and will take a bit longer to run. to further this problem. The OS doesn’t fully optimize the CPU's this way. and there are some intermittent threads that make it onto Core 1.
CPU1: AABCABDAAAACDA
CPU2: BCDBCDBCDBCDBCDBCD
The game is still slowed down even more by the other CPU intensive applications.

8O :?: Confused me a bit here... Isn't this:
CPU1: AABCABDAAAACDA
CPU2: BCDBCDBCDBCDBCDBCD

better than trying to run AABCABDAAAACDA AND BCDBCDBCDBCDBCDBCD on just 1 CPU?

Technically it's CPU0 and CPU1

 

[mpasternak]

4. Seems to good to be true, What’s the Downside?
A> while they handle multiple threads well, Single threaded applications will still only use 1 core / 1 CPU at a time, Leaving the 2nd CPU core often underused or not used at all. Games in particular are virtually all single threaded. (We’ll call thread A)
CPU1:AAAAAAAA
CPU2:BCDBCDBCDBCDBCDBCDBCDBCD
What ya can see that if you set the game to use up an entire Core, yes, you can run other threads on the 2nd core without a hit to the game performance. BUT those background threads will all have to share the 2nd core and will take a bit longer to run. to further this problem. The OS doesn’t fully optimize the CPU's this way. and there are some intermittent threads that make it onto Core 1.
CPU1: AABCABDAAAACDA
CPU2: BCDBCDBCDBCDBCDBCD
The game is still slowed down even more by the other CPU intensive applications.

8O :?: Confused me a bit here... Isn't this:
CPU1: AABCABDAAAACDA
CPU2: BCDBCDBCDBCDBCDBCD

better than trying to run AABCABDAAAACDA AND BCDBCDBCDBCDBCDBCD on just 1 CPU?

Thats a very qood question. technically YES it is better to run them over the two cores. but you get into the main question. WHAT do you want your computer to do?

a pure gamer when gaming will want only A running, and it running as fast as humanely possible. the best way to do that is shut down BCD completely so that only A is in use. tahts why for gaming you will get the best performance out of a faster single core processor when the game is the only thing running. the problem with the games is that they are virtually all limited to ONE thread so far. so the games themselves don't take advantage of the multi core. they just want ONE realy realy realy fast core.

where this comes into play is really the best BANG for the BUCK.
lets look into current newegg prices for the CPU's for this example. ( I will use AMD CPu's since they are Currently the better of the two manufacturers)

Athlon64 3700+. 2.2ghz w 1mb cache
This CPU gives you 2.2ghz of gaming performance for a single thread. single core. $235.

rembering that Gaming is single threaded and needs the fastest CPU for one thread only. the dualcore CPU that offers 2.2ghz for a game though is this one.

4400 X2. 2.2ghz each core. 1mb cache. $497

so given the CPU Speeds. to get the same in game performance as a 3700+ @ 2.2ghz you need a dual core CPU thats almost than double the price.

Dualcore DOES have it's merits though. if you CAN afford it and need it and do true multitasking. than yes it definately makes more sense

and multitasking isnt simply running multiple applications. that sit waiting for input. true multi-tasking is running multiple applications that will truly utilize CPU even while doing other things with multiple threads.

Running a Game as well as running some sort of compiling is multi tasking.

Running MS Word and MSN messenger... not so much.

and dual core itself wjill help with more than just multitasking. single tasks that use multiple threads will benefit greatly

 

[TimidKiller]

Wow!! Thanks for the elaborate response, but my numbers tell abit of a different story. I initially setup my gaming system with the 4000+, but since I had started to do more transcoding, I felt dual core was needed. Here are my numbers from 3DMARK05:

3800+(X2) @ 2.4ghz / 7800gtx 256mb(490/13100) = 8635
4000+ @ 2.7ghz / 7800gtx 256mb(490/13100) = 8589

Then I went SLI!!!

3800+(X2) @ 2.37ghz/ 7800gtx 256mb(490/13100) SLI = 12047
4000+ @ 2.64ghz / 7800gtx 256mb(490/13100) SLI = 12249

My memory is Corsair XMS Twinx2048-3200c2pt 2-3-3-6-1T

There's really not a big difference in the numbers when I compared the 2, but for me I felt the 3800+ was smoother although they performed about the same in my setup. Only thing is that in your comparison you compared a 2.2ghz single core to a 2.2ghz dual core, but my numbers don't scale in the same way. According to your example, if I compared a 2.4ghz dual core to a 2.4ghz single core (in terms of just gaming) they should be on par, but my numbers are telling me that a 2.4ghz X2 benches in the ball park of an FX-55.... curious

 

[zeezee]

The OS doesn’t fully optimize the CPU's this way. and there are some intermittent threads that make it onto Core 1.
CPU1: AABCABDAAAACDA
CPU2: BCDBCDBCDBCDBCDBCD
The game is still slowed down even more by the other CPU intensive applications.

Are you sure that this is a drawback of dual cores? I don't understand what would be different if you ran the same threads on a single core so that your game would run faster.

But when you get into something like gaming where the game requires intensive use of 1 CPU only, you run into a situation of the OS / Thread scheduler not appropriately controlling the threads for maximum performance.

What exactly is inappropriate thread control here?

Often gaming performance is either sacrificed while the CPU evenly assigns other threads to the CPU the games using,

Once again what would be different with single core/same threads?

or the 2nd CPU runs mostly idle or underused because you don't run anything else while running the game.

...like don't buy a Porche as you won't be driving it at 120 all the time.

 

[zeezee]

Another question while we are at it.

Do you tink there is a performance difference between the following two scenarios?

AAAAAAAAAAAAA
BBCCDDBBCCDD

and

BBAAAAAACCAA
AACCDDBBAADD

 

[RoundSparrow]

Another question while we are at it.

Do you tink there is a performance difference between the following two scenarios?

AAAAAAAAAAAAA
BBCCDDBBCCDD

and

BBAAAAAACCAA
AACCDDBBAADD

Yes, there could be if there is shared communications between threads. Two threads on same CPU share cache vs. going to slower main system RAM on multiple CPU's.

None of this is new... multi-CPU system behavior has been documented for decades. There were even Pentium 3 systems with as many as 16 cpu's "Dual Core" doesn't change the rules that much.

 

[zeezee]

Yes, there could be if there is shared communications between threads. Two threads on same CPU share cache vs. going to slower main system RAM on multiple CPU's.

The topic is dual cores so let's stick to them as with AMD it makes a theoretical difference due to using the crossbar switch instead of the system bus which is I think what you meant above.

But in real life, how many times does a thread to thread communication occur and on dualies and how many times does one of the cashes become outdated exactly at the time that the scheduler switches threads?

I believe not enough to justify a remark like "Gamers shouldn't buy dualies as they run slower because of the scheduler".

Surely, dual cores for games are not recommended but the reason are more likely immature environment like chipsets, XP (more directx than thread scheduler), drivers, etc.