ejolson
Posts: 9483
Joined: Tue Mar 18, 2014 11:47 am

Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 12:53 am

ejolson wrote:
Thu May 28, 2020 10:35 pm
trejan wrote:
Thu May 28, 2020 10:21 pm
pagenotfound wrote:
Thu May 28, 2020 9:57 pm
Does anybody know whether the speed of the RAM is higher compared to the 2/4 GB models?
The specifications page on raspberrypi.org still says LPDDR4-3200 so it is likely to be the same as before. The new 8GB part is rated for a higher clock but the 1/2/4GB Pi 4 boards never ran the RAM at the maximum possible clock anyway.

Code: Select all

2GB = D9WHZ = MT53D512M32D2DS-053 WT:D = 16Gb 1866MHz
4GB = D9WHV = MT53D1024M32D4DT-053 WT:D = 32Gb 1866MHz
8GB = D9ZCL = MT53E2G32D4NQ-046 WT:A = 64Gb 2133MHz
It can be confirmed by running "vcgencmd measure_clock pllh" on an 8GB Pi.
As explained here

viewtopic.php?f=63&t=271121#p1644747

one of the main constraints to parallel scaling in the Pi memory subsystem is how many rows of RAM can be open at a time and across how many banks can reads and writes be scattered.

If someone who has an 8GB Pi could run the parallel stream benchmark using the script posted in

viewtopic.php?f=63&t=271121#p1644489

that would determine whether the 8GB chip leads to better performance.
For what it's worth, Tom's Hardware has made a simple memory test comparing the 8GB model to the 4GB one.

Image
https://www.tomshardware.com/news/raspb ... 8gb-tested

While the axis on the graph is confusing, the performance appears identical to within 1 percent. I wonder if the parallel scaling of the stream benchmark is also the same.

Heater
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Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 1:05 am

Those tests miss the point about what it is that having more RAM might speed up. Integer and float performance is not one of them. Unless you are dealing with data sets that won't fit in 4GB.
Memory in C++ is a leaky abstraction .

W. H. Heydt
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Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 1:07 am

epoch1970 wrote:
Thu May 28, 2020 11:20 pm
W. H. Heydt wrote:
Thu May 28, 2020 10:38 pm
Another answer to the OPs basic question is: Because they can.
And in the instance I would rephrase that as: “if you could, you would too.”

4 “contributions” on the same topic, perhaps a 100 lines in, how many consummate answers are enough?
It's like the old joke about economists...it you laid them end to end, they'd all point in different directions. Or Harry Truman's complaint about the same profession, he wanted someone to send him a one-armed economist.

ejolson
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Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 1:18 am

Heater wrote:
Fri May 29, 2020 1:05 am
Those tests miss the point about what it is that having more RAM might speed up. Integer and float performance is not one of them. Unless you are dealing with data sets that won't fit in 4GB.
I think those are copy operations using either an integer or floating point data type. Before the epidemic, floating point registers had the advantage of a longer word length and the resulting copy loop often ran much faster.

These days 64-bit integers are common as well as 128-bit NEON. According to Tom, floating point is slower by a couple percent. As the copy loops are likely only a few lines of assembler, it would be interesting to see the exact code.

Note, compared to the 5511.8 MB/s copy speed obtained with stream for the 4GB Pi 4B in the table summarised here

viewtopic.php?t=271121#p1643919

Tom's memory results look rather slow.
Last edited by ejolson on Fri May 29, 2020 2:13 am, edited 6 times in total.

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Gavinmc42
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Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 1:54 am

Someone who has only posted 4 times does not have enough knowledge.

I guess the original Pi4 data booklet is now correct.
New camera, new Pi4 8GB, new 64bit OS, new USB boot loader, not even Xmas yet.

Edit, Eben says Vulkan news soon. It is Xmas.
Looks like Lockdown is productive for the RPF?
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges

ronnymorrissey
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Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 2:18 pm

I’m unsure why you have to be so chippy with me? It is my and others constant purchases of a raspberry pi that keep you in employment. I am allowed to be critical without you berating me for it and I’m allowed to stand by my view.
jamesh wrote:
Thu May 28, 2020 4:51 pm
ronnymorrissey wrote:
Thu May 28, 2020 3:28 pm
PeterO wrote:
Thu May 28, 2020 3:13 pm
No one is forcing you to buy one. Maybe another brand would meet your requirements better.
PeterO
I love the Pi. I am a huge fan and use them daily. The Pi4 4gb model and processor and form factor is hugely impressive. I’m adding that caveat because I feel one can criticize something that raspberry pi has done without being a ‘hater’ or ‘ungrateful’.

Again I will posit the question as to why an 8gb model has been released without a processor upgrade? Surely at some point processor speed has to catch up with memory?
OK, since you seem to have ignored my previous post which did explain this, I;ll add a bit more detail.

The cost of developing a new more powerful SoC is probably in excess of $10 MILLION, at least. Not only that but the one on the Pi4 took, IIRC more than 3 years to develop. Raspberry Pi do not design or make SoC's either, so we rely on a third party to design and make those chip. THEN add on the development cost of designing a new PCB to use that chip, probably another million or 2, that's is down to us. THEN add on the cost of the software support to get that new board and SoC working, also down to us. That's also another year or two's work.

Compare that with simply changing the RAM chip on the current model. Cost? $200k? (that a guess, but probably the right ballpark), time to market less than 6 months.

Do you get it now?

Extra RAM gives a boost to people with use cases that need a lot of RAM, and in those circumstances the speed up is considerable. If you don't need it, then you don't need it! For example, I do not have an 8GB Pi. Because I don't need 8GB of RAM. 4GB is fine for my purposes.

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PeterO
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Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 2:44 pm

Gavinmc42 wrote:
Fri May 29, 2020 1:54 am
Someone who has only posted 4 times does not have enough knowledge.
Certainly not long enough not to argue with James :-)
PeterO
Discoverer of the PI2 XENON DEATH FLASH!
Interests: C,Python,PIC,Electronics,Ham Radio (G0DZB),1960s British Computers.
"The primary requirement (as we've always seen in your examples) is that the code is readable. " Dougie Lawson

jamesh
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Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 3:50 pm

ronnymorrissey wrote:
Fri May 29, 2020 2:18 pm
I’m unsure why you have to be so chippy with me? It is my and others constant purchases of a raspberry pi that keep you in employment. I am allowed to be critical without you berating me for it and I’m allowed to stand by my view.
jamesh wrote:
Thu May 28, 2020 4:51 pm
ronnymorrissey wrote:
Thu May 28, 2020 3:28 pm


I love the Pi. I am a huge fan and use them daily. The Pi4 4gb model and processor and form factor is hugely impressive. I’m adding that caveat because I feel one can criticize something that raspberry pi has done without being a ‘hater’ or ‘ungrateful’.

Again I will posit the question as to why an 8gb model has been released without a processor upgrade? Surely at some point processor speed has to catch up with memory?
OK, since you seem to have ignored my previous post which did explain this, I;ll add a bit more detail.

The cost of developing a new more powerful SoC is probably in excess of $10 MILLION, at least. Not only that but the one on the Pi4 took, IIRC more than 3 years to develop. Raspberry Pi do not design or make SoC's either, so we rely on a third party to design and make those chip. THEN add on the development cost of designing a new PCB to use that chip, probably another million or 2, that's is down to us. THEN add on the cost of the software support to get that new board and SoC working, also down to us. That's also another year or two's work.

Compare that with simply changing the RAM chip on the current model. Cost? $200k? (that a guess, but probably the right ballpark), time to market less than 6 months.

Do you get it now?

Extra RAM gives a boost to people with use cases that need a lot of RAM, and in those circumstances the speed up is considerable. If you don't need it, then you don't need it! For example, I do not have an 8GB Pi. Because I don't need 8GB of RAM. 4GB is fine for my purposes.
You have your view, I explained why it was in error, then you asked again, and I explained, again, in more detail.

Everyone, of course, is entitled to an opinion. (Except, no they probably are not https://qz.com/852709/a-philosophy-prof ... r-opinion/). But please don't get upset if people think that opinion is wrong, and tell you why.
Principal Software Engineer at Raspberry Pi Ltd.
Working in the Applications Team.

ejolson
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Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 5:56 pm

PeterO wrote:
Fri May 29, 2020 2:44 pm
Gavinmc42 wrote:
Fri May 29, 2020 1:54 am
Someone who has only posted 4 times does not have enough knowledge.
Certainly not long enough not to argue with James :-)
PeterO
It may be a mistake to think posting to this forum increases knowledge. Then again some of the answers here do contain information and are not chippy.

I don't think anyone should be arguing whether faster or slower processors are better. As far as I can tell, the person who made the original post was being less chippy than many of the replies.

Having said this, it is interesting that a manufacturer of similar single-board computers just introduced a new model this week that instead of more memory has memory bandwidth twice that of the 4GB Pi 4B. However, the processor used by that other computer is a Cortex-A55, which turns out to be slower even though clocked faster.

From this point of view, the CPU speed of the Pi 4B already weighs much more in the balance between memory than on some other systems. Of course every application requires a different balance of system resources to run well. Some may prefer a faster CPU, some faster RAM, others more RAM while others are dependent on networking or storage.

If I had the team and resources to create an original design, I would focus on ECC memory. As it is, development of the BARK™ system has stalled out during the epidemic and the main engineer is now working on an 8-bit POC with power needs in the sub-milliwatt range.

Heater
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Re: Why release an 8gb model without upgrading the processor?

Fri May 29, 2020 6:14 pm

Never mind the "chippy" people.

Think of it like a kind of induction. Like a new kid in school or new recruits in the army. For whatever reason the older kids have the urge to test your metal and set you straight, as it were. You soon get the hang of it.
Memory in C++ is a leaky abstraction .

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Gavinmc42
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Re: Why release an 8gb model without upgrading the processor?

Sat May 30, 2020 10:47 am

I have never bothered but I think some have overclocked to 2GHz.
That is a 33% upgrade. Cooling required.
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges

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