Re:Apple M1 foreshadows Rise of RISC-V
by socialdemocrat on Sunday December 20, 2020 @06:05AM
(#25485414)
Very interesting comment. I mean you see some of the same things with companies like Tesla also pushing vertical integration.
A lot of the examples you see are similar to what you talk about. You can cut down on the friction between different parts.
I remember an example of software controlling a blinking icon on the dashboard, where this was a 10 minute code change for Tesla but a 2-3 month update cycle for a traditional automaker due to the dashboard hardware coming from a supplier.
If we're comparing the M1 to x86, though, then all the prefetching and other memory shenanigans are on the CPU die. The A1 had an advantage over the SoCs used in Android phones here, but the M1 doesn't have an advantage over Intel and AMD CPUs.
In the case of the memory prefetcher story, this was about other ARM CPUs, which the M1 and A-series have left completely in the dust some years ago.
Re:Apple M1 foreshadows Rise of RISC-V
by bloopernova on Sunday December 20, 2020 @06:35AM
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May I ask what your opinion is on the NVidia ARM purchase?
Re:Apple M1 foreshadows Rise of RISC-V
by aledthemathguy on Sunday December 20, 2020 @06:48AM
(#25485628)
thanks for sharing this. you are an insider. did u think of putting your knowledge on writing? i will sure like to read that kind of content :)
> the partners (Samsung, Qualcomm etc) are the ones implementing the SoC and hence controlling the wider memory system.
And I assume the partners also do some things differently, for at least somewhat legitimate reasons, and no one ARM design can be optimal for everyone.
Nvidia makes arm processors, GPUs and SoCs, so this integration will be good for them if the arm sale is approved.
You use the word partner with the proper noun Qualcomm but there are no quotes. Qualcomm's only focus is to make money while delivering the worst experience in every direction. They are often stuck in local maximums and they are too big to just flow around.
? shared prefetch queue ?
I think the vertical integration they have is a major advantage too.
I used to work at arm on CPUs. One thing I worked on was memory prefetching which is critical to performance. When designing a prefetcher you can do a better job if you have some understanding or guarantees as to the behaviour of the wider memory system (better yet if you can add prefetching specific functionality to it). The issue I faced is the partners (Samsung, Qualcomm etc) are the ones implementing the SoC and hence controlling the wider memory system. They don't give you detailed specs of how that works, nor is there an method where you can discuss with them appropriate ways to build things to enable better prefetching performance. You end up building something that's hopefully adaptable for multiple scenarios and no one ever gets a chance to do some decent end to end performance tuning. I'm either working with a model of what the memory system might be and Qualcomm/Samsung etc engineers are working with the CPU as a black box trying to tune their side of things to work better. Were we all under one roof I suspect we could easily have got more out of it.
You also get requirements based upon targets to hit for some specific IP, rather than requirements around the final product, e.g. silicon area. Generally arm will be keen to keep area increase low or improve performance / area ratio without any huge shocks on overall area. If you're apple you just care about the final end user experience and the potential profit margin. You can run the numbers and realise you can go big on silicon area and get where you want to be. With a multi-company/vendor chain each link is trying to optimise for some number they control, even if that overal has a negative impact on the final product.