Discussion Qualcomm Snapdragon Thread

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Nothingness

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I remind people that one of the reasons Andrei left this forum (not AT) was constant unfounded criticisms by some here. OTOH I guess he could not tell us much anyway due to where he works now.
 

Nothingness

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DisEnchantment

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Unless I missed something it's the dispatch width which is 14 uops. It's not the same as a 14 wide instruction decoder.
Dispatch width is extremely wide. Since there is no uop cache those uops should come fully from instruction decode. Compared to 6 vs Z4 or 8 for Z5. But not apples to apples comparable
Same mis-predict penalty vs Z4
Same L1 latency vs Z4
It has lower latency for vector (neon), but not apples to apples comparable vs x86 vector
ROB is surprisingly conservative for a 2024 core.

Similar amounts of LS and ALU ports compared to Z5, although Z5/Z4 has two additional FP ports. Store and Load queues depths comparable to Z4.
Not sure how branch address are calculated, for instance Z5 has 4 AGUs for those

It looks OK, nothing in particular stands out. If it is mostly an efficiency play then we will see soon.
 
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Nothingness

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Dispatch width is extremely wide. Since there is no uop cache those uops should come fully from instruction decode. Compared to 6 vs Z4 or 8 for Z5. But not apples to apples comparable
That can be quite complex: uops are stored in queues between decoder and dispatch; also a decoder could emit two uops per cycle. For instance a mem operation with writeback can be split in two uops, one going into ALU queue(s) for the writeback of the base register, while the other goes into load/store queue(s). So I'm afraid at this point nothing can be guessed about decoder width (though I agree it's surely wide, but it's unlikely to be 14-wide).

I've often been wrong, so I won't exclude I'm wrong again

Same mis-predict penalty vs Z4
Same L1 latency vs Z4
It has lower latency for vector (neon), but not apples to apples comparable vs x86 vector
ROB is surprisingly conservative for a 2024 core.

Similar amounts of LS and ALU ports compared to Z5, although Z5/Z4 has two additional FP ports. Store and Load queues depths comparable to Z4.
Not sure how branch address are calculated, for instance Z5 has 4 AGUs for those

It looks OK, nothing in particular stands out. If it is mostly an efficiency play then we will see soon.
I agree with you on all these points. Can't wait to see the reverse engineering of the uarch details by talented hackers! And benchmarks.

PS - A writeback operation in AArch64 is for instance a ldr x0, [x1], #8 which will do the load then add 8 (size of x0) to x1.
 
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SarahKerrigan

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That can be quite complex: uops are stored in queues between decoder and dispatch; also a decoder could emit two uops per cycle. For instance a mem operation with writeback can be split in two uops, one going into ALU queue(s) for the writeback of the base register, while the other goes into load/store queue(s). So I'm afraid at this point nothing can be guessed about decoder width (though I agree it's surely wide, but it's unlikely to be 14-wide).

I've often been wrong, so I won't exclude I'm wrong again


I agree with you on all these points. Can't wait to see the reverse engineering of the uarch details by talented hackers! And benchmarks.

PS - A writeback operation in AArch64 is for instance a ldr x0, [x1], #8 which will do the load then add 8 (size of x0) to x1.

There's also fusion to consider. As you know, "width" is kind of a fuzzy concept, especially with aggressively OoO machines where number of uops executing in a given cycle can greatly exceed the machine's sustained whole-pipe width.

Note that Neoverse V2, which is emphatically an 8-wide core, is listed as 16-wide in its LLVM machine model. Vendors tend to do the high-level machine-model variables in their own unique ways, often based on quantitative analysis on codegen rather than on the uarch manual.
 

soresu

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Dec 19, 2014
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Went back to that ARM rumor site and found something odd under Cortex X6:


Implication seems to be a new core IP segment between X and A7xx starting with this 'Alto'.

Not sure if this is just a bad translation or not.
 

Nothingness

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For people with too much money on their hands, there's a board with a Cortex-X3 based Qualcomm SoC:

The TurboX SOM specification: https://thundercomm.s3.ap-northeast...0-en]_TurboX_C8550_SOM_Product_Brief_V1.0.pdf

Qualcomm® QCS8550
Kryo™ CPU
Adreno™ 740 GPU
GPU Spectra™ ISP
12GB
QCS8550: https://docs.qualcomm.com/bundle/pu..._QCS8550_QCM8550_PROCESSORS_PRODUCT_BRIEF.pdf

Qualcomm® Kryo™ CPU; 64-bit architecture
- 1 Prime core, up to 3.36 GHz with Arm® Cortex®-X3 technology
- 4 Performance cores, up to 2.8 GHz
- 3 Efficiency cores, up to 2.0 GHz

$1600 with only 12 GB is way too much for my toying needs
 
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SarahKerrigan

Senior member
Oct 12, 2014
383
562
136
For people with too much money on their hands, there's a board with a Cortex-X3 based Qualcomm SoC:

The TurboX SOM specification: https://thundercomm.s3.ap-northeast-1.amazonaws.com/uploads/web/c8550/[tc-P-1110-en]_TurboX_C8550_SOM_Product_Brief_V1.0.pdf


QCS8550: https://docs.qualcomm.com/bundle/pu..._QCS8550_QCM8550_PROCESSORS_PRODUCT_BRIEF.pdf



$1600 with only 12 GB is way too much for my toying needs

Embeddedified Snapdragon 8g2, looks like. A little steep for me as well, though certainly quick.
 
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