Multitasking, physical core vs virtual cores

[nyker96]

here's an interesting benchmark that pits virtual cores vs physical cores in multitasking:

http://www.tomshardware.com/reviews/gaming-processor-core-i3-athlon-ii,2666-10.html

of course the results are somewhat expected, still interesting to see some hard numbers.

 

[santz]

where is the i5 and i7? it only benchmarks the i3 against amd and older cpu's

 

[Lonyo]

i5 750 vs equal clocked i5 6xx would make more sense. 4C/4T vs 2C/4T

 

[IntelUser2000]

Come on Toms! Nobody who plays games runs another equally demanding app in the background. These are one of the reasons some criticize Tomshardware of degraded quality in reviews.

At least do multi-tasking with two apps which do not include gaming.

 

[Lonyo]

Come on Toms! Nobody who plays games runs another equally demanding app in the background. These are one of the reasons some criticize Tomshardware of degraded quality in reviews.

At least do multi-tasking with two apps which do not include gaming.

Actually, some people do, but not the sort of app they tested.
What would be interesting would be to check out running a game while running screencapping software (i.e. recording the game).
That's a real-world multitasking scenario involving gaming and another somewhat stressful task (although not necessarily on the CPU, but it does take cycles, plus it involves lots of I/O).

 

[Scali]

I think the comparison between virtual and physical cores is completely irrelevant.
Namely, virtual cores are ADDED to a physical dualcore or quadcore.
They don't require a lot of extra logic and don't use a lot of extra power.
So the real value of virtual cores is that they give you EXTRA processing power and multitasking capabilities at very low additional cost, both in CPU price and power consumption.
So you should compare eg a dualcore with HT against a dualcore without HT of the same price (probably slightly higher clocked). That's when you can measure the true value of the technology, and then it balances out nicely. It improves performance/watt and price/performance ratios.

 

[beginner99]

So you should compare eg a dualcore with HT against a dualcore without HT of the same price (probably slightly higher clocked). That's when you can measure the true value of the technology, and then it balances out nicely. It improves performance/watt and price/performance ratios.

I would say you can actually see that because the Pentium G6950 takes a much bigger hit than the i3 versions at least in Avg. framerate.
And yes it's stupid to compare real cores with virtual ones using different architectures.

 

[0roo0roo]

Come on Toms! Nobody who plays games runs another equally demanding app in the background. These are one of the reasons some criticize Tomshardware of degraded quality in reviews.

At least do multi-tasking with two apps which do not include gaming.

sometimes i run a video or h264 720/1080p vid on a second screen while gaming, sometimes even time stretched. yes there are legal ones even...revision 3 for example whats missing is how fast that rar is being compressed.

 

[0roo0roo]

I think the comparison between virtual and physical cores is completely irrelevant.
Namely, virtual cores are ADDED to a physical dualcore or quadcore.
They don't require a lot of extra logic and don't use a lot of extra power.
So the real value of virtual cores is that they give you EXTRA processing power and multitasking capabilities at very low additional cost, both in CPU price and power consumption.
So you should compare eg a dualcore with HT against a dualcore without HT of the same price (probably slightly higher clocked). That's when you can measure the true value of the technology, and then it balances out nicely. It improves performance/watt and price/performance ratios.

the additional cost is not minimal, you pay the intel premium

 

[Scali]

the additional cost is not minimal, you pay the intel premium

Yea, and back when AMD was the fastest (I can barely remember), you paid the AMD premium, boohoo. Performance has its price, period. Any commercial company would be stupid not to demand a premium when they have the upper hand.

 

[classy]

i5 750 vs equal clocked i5 6xx would make more sense. 4C/4T vs 2C/4T

Yea this would have been a better scenario. But its been known since the days of P4 with hyper-threading that physical cores have higher performance over virtual cores when using more than one app.

 

[taltamir]

Yea, and back when AMD was the fastest (I can barely remember), you paid the AMD premium, boohoo. Performance has its price, period. Any commercial company would be stupid not to demand a premium when they have the upper hand.

i still remember 1000$ AMD CPUs

 

[evolucion8]

Yeah, that's why in heavily multi threaded scenarios, a Thuban with 6 real cores which offers 50% more performance than a similar Phenom II X4, can match the i7 860 which has 4C with 8T, which offers 50% more performance than a similar i7 750 which doesn't have Hyper Threading at all.

 

[Scali]

Yeah, that's why in heavily multi threaded scenarios, a Thuban with 6 real cores which offers 50% more performance than a similar Phenom II X4, can match the i7 860 which has 4C with 8T, which offers 50% more performance than a similar i7 750 which doesn't have Hyper Threading at all.

That depends on what 'multi threaded scenario' you're talking about.
With HT, the i860 can juggle 8 threads at a time, where Thuban can only hold 6 threads in the air simultaneously.
With virtualization HT tends to scale better, because having more threads in the air at the same time is more important than the absolute amount of processing performance available to each thread.
Sun's Niagara CPU is designed specifically for such scenarios, taking SMT a step further than Intel's HT. In the absolute sense, it's not such a powerful CPU. But because of the massive amount of threads it can handle simultaneously, it's very interesting for virtualization servers and such. You get low response times for webservers or databases, with lots of simultaneous requests.

 

[evolucion8]

Yeah, but remember than in Thuban, each thread doesn't share its execution resources, with Hyper Threading, two threads shares everything like cache and execution engine resources, and they tends to fight each other for resources, causing cache trashing. That's why you never saw the i7 860 scaling 100% faster than a similarly clocked i7 750 or even a Q9650. Having more threads in the air doesn't mean much if they have to share execution resources. Hyper Threading only duplicates the architectural state, doesn't duplicate execution resources. Niagara CPU is much wider than anything Intel has currently.

Multi threaded scenario can be anything, like WinRaR, Nero Encoding, Cinebench, etc.

 

[Scali]

Yeah, but remember than in Thuban, each thread doesn't share its execution resources, with Hyper Threading, two threads shares everything like cache and execution engine resources, and they tends to fight each other for resources, causing cache trashing.

Did you bother to read my post? I think I covered that quite well.

 

[evolucion8]

Did you bother to read my post? I think I covered that quite well.

No, you didn't Virtual cores will never outperform real cores unless if they're terrible innefficient, and yet, look at the Pentium 4.

 

[Scali]

No, you didn't Virtual cores will never outperform real cores unless if they're terrible innefficient, and yet, look at the Pentium 4.

I guess the whole Sun Niagara bit went way over your head then?

 

[aigomorla]

Come on Toms! Nobody who plays games runs another equally demanding app in the background. These are one of the reasons some criticize Tomshardware of degraded quality in reviews.

At least do multi-tasking with two apps which do not include gaming.

*raises hand*

Actually i do a lot while gaming, which is why i have a hexcore. D:

 

[jaqie]

sometimes i run a video or h264 720/1080p vid on a second screen while gaming, sometimes even time stretched. yes there are legal ones even...revision 3 for example whats missing is how fast that rar is being compressed.

Bingo. Exactly.

Thank you for posting what I was going to say for me

 

[evolucion8]

I guess the whole Sun Niagara bit went way over your head then?

No, your stubborness did.

Niagara is a different architecture with a different feature set and can't be compared directly. I'm talking about x86 vs x86.

 

[Scali]

Niagara is a different architecture with a different feature set and can't be compared directly. I'm talking about x86 vs x86.

The point of Niagara is that a single physical core is considerably less powerful than a single Nehalem core, while Niagara has 8-way SMT per core, rather than 2-way, like Nehalem does.
Apparently in certain multitasking scenarios this makes perfect sense. Because as I said: "having more threads in the air at the same time is more important than the absolute amount of processing performance available to each thread".
Which already pre-emptively countered your arguments of "Yeah, but remember than in Thuban, each thread doesn't share its execution resources, with Hyper Threading, two threads shares everything like cache and execution engine resources, and they tends to fight each other for resources, causing cache trashing."
There's considerably more fighting for resources going on in Niagara than in Nehalem, and still it's a fine CPU.

The key to Niagara is not that its virtual cores are terribly fast. The key is that they can put so many of these cores on a single die.
Intel's HT is far less extreme, but the idea is similar: You can get a CPU with 8 or 12 simultaneous threads, something that no other x86 CPU can do (okay, with the exception of Magny Cours, but at the cost of two large, powerhungry chips. Intel could fit far more threads in that same size and power envelope, using HT).
That's the extra value of HT: you get more simultaneous threads at the same cost.

 

[IntelUser2000]

Having more threads in the air doesn't mean much if they have to share execution resources. Hyper Threading only duplicates the architectural state, doesn't duplicate execution resources. Niagara CPU is much wider than anything Intel has currently.

?? Sun's Niagara is a 1-issue wide CPU. It's even narrower than the Atom/Cortex Ax/original Pentium etc.

The bold part is the important part. They only duplicate the register stack and the return state which takes nearly nothing to do in terms of die size. They claimed less than 5% die area for the Northwood based Pentium 4 core(not even die), Nehalem is far larger than that. Think of how much 20-30KB of SRAM takes in die space using 45nm/32nm.

Without Hyperthreading Phenom II X6 would have been faster than everything except the 980X.

 

[LoneNinja]

*raises hand*

Actually i do a lot while gaming, which is why i have a hexcore. D:

I second that, except I haven't bought a cpu since December and hexcores weren't around at the time. It annoys me to close programs I have running so I can play a game, to bad I'm forced to do so occasionally because all I have is an X4. lol

 

[Scali]

The bold part is the important part. They only duplicate the register stack and the return state which takes nearly nothing to do in terms of die size. They claimed less than 5% die area for the Northwood based Pentium 4 core(not even die), Nehalem is far larger than that. Think of how much 20-30KB of SRAM takes in die space using 45nm/32nm.

Yes, that exactly (and where has the post you replied to gone?).
With the addition of just a small amount of logic, you enable extra parallelism and boost the efficiency of the execution backend.
I already said it before:
"Namely, virtual cores are ADDED to a physical dualcore or quadcore.
They don't require a lot of extra logic and don't use a lot of extra power.
So the real value of virtual cores is that they give you EXTRA processing power and multitasking capabilities at very low additional cost, both in CPU price and power consumption.
...
It improves performance/watt and price/performance ratios."

It's no coincidence that Sun and IBM are both using SMT aswell. You could say that AMD is the odd one out. The only major server/workstation CPU manufacturer that doesn't have SMT.