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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Desktops > iMac going sixcore

iMac going sixcore
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Aug 23, 2017, 09:12 AM
 
Intel has released some early information on the next generation of CPUs, known as Coffee Lake. Release date is supposedly in October. This is still not 10nm chips but rather another tweak of the same 14nm process we have been getting chips from for close to three years now. To show a real upgrade, they're upping the core counts off its Core chips: i3 is now 4C/4T, i5 is 6C/6T, and i7 is 6C/12T. Since Apple generally uses the i5 and i7 desktop chips in its iMacs, we appear to be headed for a sixcore future.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
And.reg
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Aug 23, 2017, 09:57 AM
 
Honestly I'd rather see major improvements to CPU clock speed than stacking CPU cores. I'd like the industry to move that to the GPU and work on making, like, 2-core 10 GHz processors that don't require any more throttling than current technology amends. We have 7nm coming online soon... so, why are we still stuck with a max of 4 GHz after 10 years anyway? A lot of long-loop recursive integrations and data sorting could really benefit from faster CPUs (and larger cache). At least let's try for a max turbo of something like 6 GHz in limited process and start stepping it up.
( Last edited by And.reg; Aug 23, 2017 at 10:08 AM. )
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analogika
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Aug 23, 2017, 10:38 AM
 
What do you need that single-core performance for? What single-threaded performance bottlenecks have you experienced?
     
And.reg
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Aug 23, 2017, 11:13 AM
 
Originally Posted by analogika View Post
What do you need that single-core performance for?
I already addressed this in my above post.

Originally Posted by analogika View Post
What single-threaded performance bottlenecks have you experienced?
What do you intend to mean by your use of "bottleneck"?
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reader50
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Aug 23, 2017, 11:18 AM
 
We may have AMD to thank for this. Intel has been content with 4-core chips as standard, until AMD upped the cores for a lower price.

On the other hand, chip development lead time suggests this was coming for awhile. At least as an internal option. Perhaps not the option we'd have gotten without a competitor.
     
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Aug 23, 2017, 03:41 PM
 
Originally Posted by And.reg View Post
Honestly I'd rather see major improvements to CPU clock speed than stacking CPU cores.
Everyone would. It is always better to have one CPU core that can run at 2GHz than two that can run at 1GHz. The problem is that this is no longer possible, because physics. Increasing clockspeed beyond the sweet spot makes the power requirements go up as the clockspeed cubed, which becomes untenable very quickly. This was realized by the industry about ten years ago. For Intel it meant cancelling the Pentium 4 line and retooling to Core, which took two and a half years during which time they lost a lot of business. For Apple it meant reneging on the "3GHz within a year" thing for the G5, and the best they could do was 2.5GHz with watercooling.

The only ones currently pushing clockspeed into the stratosphere are IBM, and they're doing it with their server chips that use insane amounts of power. Even so they can barely keep up with Intel's best.

Originally Posted by And.reg View Post
I'd like the industry to move that to the GPU and work on making, like, 2-core 10 GHz processors that don't require any more throttling than current technology amends. We have 7nm coming online soon... so, why are we still stuck with a max of 4 GHz after 10 years anyway? A lot of long-loop recursive integrations and data sorting could really benefit from faster CPUs (and larger cache). At least let's try for a max turbo of something like 6 GHz in limited process and start stepping it up.
See above, but on a more philosophical note: CPU design can go one of two ways, towards a "brainiac" (high IPC at low clock) or "speed demon" (low IPC at high clock). Between about 1990 and 2004, the "speed demon" designs always won. Since then, the "brainiac" designs have won, and the "speed demons" like AMDs Bulldozer designs have failed, precisely because they cannot be clocked high enough to compensate. The math might change again, but it would require a new material to make CPUs from first.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Aug 23, 2017, 03:56 PM
 
Originally Posted by reader50 View Post
We may have AMD to thank for this. Intel has been content with 4-core chips as standard, until AMD upped the cores for a lower price.

On the other hand, chip development lead time suggests this was coming for awhile. At least as an internal option. Perhaps not the option we'd have gotten without a competitor.
Oh, it is absolutely because of AMD. Zen was a shot across their bow and Intel is responding the only way they can quickly enough. The big change isn't actually that they made a sixcore chip - it is that they made the i3 quadcore. I suspect that the plan was to keep the i3 at 2C/4T, move the i5 to 4C/8T (like the old i7) and make the new i7 6C/12T. Intel can afford to make the i7 bigger - they don't sell that many, and they usually sell them with the small GPU anyway because everyone gets a discrete GPU to pair with it. The problem was that Zen offered not only an 8C/16T chip in the high-end desktop segment, but is also making value-priced quadcores that compete with the i3 and i5, and will pair those quads with some pretty decent integrated graphics soon enough. Intel was forced to step up the die sizes there, and that is going to cost them.

That they made a sixcore in the first place is probably because they needed something new when 10nm was going to be another year late, and as a hedge against Zen. It can't have been hard - most likely they reused the ring bus design from the Ivy Bridge-E chip (the smallest model was a sixcore) and updated the core design to Skylake.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Aug 24, 2017, 01:00 AM
 
Originally Posted by And.reg View Post
Honestly I'd rather see major improvements to CPU clock speed than stacking CPU cores. I'd like the industry to move that to the GPU and work on making, like, 2-core 10 GHz processors that don't require any more throttling than current technology amends.
That's not possible with the technology we have. Loooong time ago Intel tried that with the Pentium 4-based architecture, and the plan was to get to 10 GHz. That didn't pan out. They hit a heat wall, though. The highest-clocking processors (without overclocking) to my knowledge are variants of IBM's Power8 which reaches 5.0 GHz at tremendous cost and power. That is the reason everyone goes in the direction of more cores, not because they want to, but because they have to.
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Aug 25, 2017, 05:49 AM
 
The later Power designs are interesting. IBM clearly sees a market where you have fantastic single-threaded performance with a wide design, combined with SMT8 (like Hyperthreading, but with 8 threads per core) to make better use of the resourced.

And I guess I should mention... Those new quadcores at 15W will not be used by Apple in the 13" MBP. They all have the bad graphics (GT2), and Apple wants at least the next step up (GT3e), which is what they have today. My guess is that there are 28W quadcores with GT3e coming, and that Apple will use them in the TB version of the 13". They're not here yet, though.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
And.reg
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Aug 25, 2017, 07:41 PM
 
Well then it makes sense then that Intel would pump out a 6-core processor w/o frequency stepup. Kind of wonder, though, if non-pro iMac users would benefit from something like an 8-core/16-thread CPU that runs at a low clock speed, e.g., 1.6 GHz, turbo at 3 GHz, and have some low-energy cores and some high-energy that turn on/off to save power, sort of like the iPhone. Any tactful use in a prosumer desktop?
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Aug 25, 2017, 07:56 PM
 
Only use would be to keep the fan speed low, and the fan speed is already effectively zero when the CPU is clocked down as low as it goes. If you need to have cooling capacity and power circuitry to use the chip at full tilt when needed, there are no other gains.

The main reason for the low power cores that phones have is somewhat esoteric. We all use so-called out of order cores in phones now (like desktops have for a long time). Out of order cores rearrange the instructions for maximum efficiency. They're more powerful, but as long as they're on, you have to keep power on to the out of order circuitry itself. That means that they have a floor beyond which the power consumption cannot drop further as long as they're on. The low power cores used by just about everyone are basic in-order cores (more specifically, dual issue in-order cores like the original Pentium, and for that matter the Apple A4) that can drop to really low power levels by enabling only the execution units actually in use at any one time.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Aug 25, 2017, 09:02 PM
 
Originally Posted by P View Post
The later Power designs are interesting. IBM clearly sees a market where you have fantastic single-threaded performance with a wide design, combined with SMT8 (like Hyperthreading, but with 8 threads per core) to make better use of the resourced.
Yeah, it seems competitive with Intel's Xeons and have a leg up in specialized work loads. That's a pretty tough job given the competitive environment for retaining CPU design talent.
Originally Posted by P View Post
And I guess I should mention... Those new quadcores at 15W will not be used by Apple in the 13" MBP. They all have the bad graphics (GT2), and Apple wants at least the next step up (GT3e), which is what they have today. My guess is that there are 28W quadcores with GT3e coming, and that Apple will use them in the TB version of the 13". They're not here yet, though.
Yup, I've been waiting for 4 cores in a 13 inch form factor for literally years!
Originally Posted by And.reg View Post
Well then it makes sense then that Intel would pump out a 6-core processor w/o frequency stepup. Kind of wonder, though, if non-pro iMac users would benefit from something like an 8-core/16-thread CPU that runs at a low clock speed, e.g., 1.6 GHz, turbo at 3 GHz, and have some low-energy cores and some high-energy that turn on/off to save power, sort of like the iPhone. Any tactful use in a prosumer desktop?
For most workloads, especially consumer workloads, no. Even when you deal with specialized workloads, adding more cores with lower frequency could slow down overall performance. There are essentially no easy and obvious wins left, and you have to invest in parallelizing software, making use of specialized hardware for specific, common workloads (such as media en/decoding and en/decryption) and so forth.

Even in a professional context, this is true: my colleagues are running simulations, one on a newer 6-core 3.33 GHz machine and another on a 16-core 2.0 or 2.2 GHz Xeon that lag one generation behind (don't remember the exact frequency) with software that is parallelized to some degree. The 6-core machine is roughly twice as fast and due to licensing restrictions, we can't run several instances in parallel.
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Aug 25, 2017, 10:28 PM
 
Has anyone heard rumors of Apple testing AMD CPUs? I'm sure they have all along, and have stuck with Intel so far. But any exclusive agreement with Intel during the PPC-x86 transition will have long since expired. And from what I've read, AMD has some pretty good offerings today. At excellent prices.

Apple used to alternate GPUs between nVidia and ATi. It would be interesting if they did the same with CPU choices. So providers need to compete.
     
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Aug 26, 2017, 07:22 AM
 
Right now AMD has basically one good CPU: Ryzen. It has 8 cores spread into two quadcore clusters and uses something called Infinity Fabric to communicate between the clusters. AMDs plan is to use this IF for all sorts of core counts, and they have 16-core and 32-core versions that are just multiple dies linked together.

This means that right this minute, the AMD are competitive in two segments: high end desktops, and the lots-of-cores-per-socket virtualization segment. Neither fits Apple all that well. They could put a high end desktop core in the iMac Pro, but that is a tiny market to risk antagonizing Intel over.

AMD has more cores coming out, in particular a quadcore with integrated graphics that is a much more mainstream choice. If that works, and if it's graphics are good enough, and if they have versions that fit into the MBP, then maybe.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Aug 26, 2017, 08:14 PM
 
AMD is only competitive in scenarios where TDP doesn't matter. I don't think I have heard them talk about very low TDP parts (15 W or 30 W mobile parts) and instead they want to be in the high-end desktop and server business thanks to the obvious synergies and similar trade-offs. Apple could put AMD's offerings in all of their desktop Macs, but they make up only a small share of the overall units that they sell. Potentially they could make the iMac Pro cheaper this way or, for very few workloads, increase performance.

Apple might be interested if they have a more complete story that includes mobile chips. If AMD wants to entice Apple to switch, I think they can do it with the graphics they put in their future mobile chips. So while Apple is clearly unhappy with Intel (stagnant CPU performance, mismatch in CPU-to-graphics performance, botched launch of last Core generation so that Apple had to skip it …), the obvious two options aren't that great either: AMD lacks mobile chips and their home-grown ARM SoCs are not powerful enough to drive the highest-end machines.
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Aug 26, 2017, 08:15 PM
 
AMD is only competitive in scenarios where TDP doesn't matter. I don't think I have heard them talk about very low TDP parts (15 W or 30 W mobile parts) and instead they want to be in the high-end desktop and server business thanks to the obvious synergies and similar trade-offs. Apple could put AMD's offerings in all of their desktop Macs, but they make up only a small share of the overall units that they sell. Potentially they could make the iMac Pro cheaper this way or, for very few workloads, increase performance.

Apple might be interested if they have a more complete story that includes mobile chips. If AMD wants to entice Apple to switch, I think they can do it with the graphics they put in their future mobile chips. So while Apple is clearly unhappy with Intel (stagnant CPU performance, mismatch in CPU-to-graphics performance, botched launch of last Core generation so that Apple had to skip it …), the obvious two options aren't that great either: AMD lacks mobile chips and their home-grown ARM SoCs are not powerful enough to drive the highest-end machines.
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Aug 27, 2017, 05:29 AM
 
Mobile Ryzen might very well be a powerful chip in that TDP. Remember that the current GPU in the MBP runs at 30W, and at that TDP, it is powerful. The GF14 process they are on seems to be quite efficient as long as you stay in the sweet spot. It is far from certain that they have something in the 15W range, especially as they don't seem to be making a dualcore version, but they could make a nice 45W chip with integrated graphics. Remember that the 15" has a 45W CPU and a 30W GPU - with 75W of TDP, you could make a lot of CPU.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Aug 27, 2017, 09:26 AM
 
Has AMD talked about its mobile Ryzen plan yet? I haven't read anything, and I thought they are focussing on Threadripper and Epyc. (Ballsy names, by the way.)
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Aug 27, 2017, 11:33 AM
 
AMD has spoken about mobile Ryzen in general terms. It is a quadcore chip (so half of Ryzen 7) with a GPU connected over IF. We know from other leaks that it is an 11 CU ( i.e. 704 shader cores) GPU, and that it uses Vega tech level. AMD also states that CPU performance is up 50%, GPU performance is up 40%, and power consumption is down "up to" 50% compare to last-gen mobile APUs. Launch date is 2H 2017.

Last gen AMD APU is a quadcore (2 modules) Excavator with 8 CUs from GCN 3 (i.e. the last 28nm chips). TDP varies a bit, but the top is 35W. CPU clock is up to 3.4 GHz at max turbo, base is 2.1 GHz. I suspect that AMD will want to keep that 35W thermal and not move the clocks very much in either direction, but move the entire thing to the modern design. Since Ryzen is more or less even with Broadwell clock for clock and thus some 5-7% behind Skylake, this will put AMD between the new U-series quadcore (28W) and the existing H-series (45W) from Intel, both on performance and thermals. Not a bad place to be.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
   
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