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by zokier
1539 days ago
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Is my understanding correct that compared to those historical architectures, modern GPUs are a lot more asynchronous? What I mean that these days you'd issue a data transfer or program execution on the GPU, they will complete at its own pace and the CPU in the meanwhile continues executing other code; in contrast in those 8 bitters you'd poke a video register or whatev and expect that to have more immediate effect allowing those famous race the beam effects etc? |
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First, in modern systems you usually don't have direct access to GPU, but call syscall and than happen magic, something like this. And they all are multilayered architecture, mean, now normal, when systrace dump of some exception lists few hundreds functions, imagine how this slow.
This is because all modern systems except consoles, are direct descendants of business minicomputers, in which where most important, they could simultaneously run wallet and text processor (or electronic table, or email, etc), and these programs will not see each others memory, so errors in text will not lead to lost money from wallet.
Second, modern systems behave like NUMA architectures, or some people even named them distributed architectures, mean, that only CPU computing in userspace is fast.
In many cases you have choice, to do magic in sync way or async, but in any case, syscalls are extremely slow, in some cases could be few magnitudes slower than userspace CPU computing.
Sometimes lifesaver some sort of message passing architecture, so you send message to GPU and immediately could do your tasks without any waits at all (kernel periodically check messages mailboxes of all processes and when happen your turn it will read your message and do things and write answer).
But message passing is now rare, mostly as I know, used paradigm of direct syscall, and async means, kernel release your process just after receive syscall, sync means, your process will be released only after syscall finished processing data.
In 8bit systems, cpu frequency where very low, sometimes fraction of bus speed and there where very few layers, basically userlevel program could directly access hardware. So even formally their behavior named synchronous, but in reality they where very fast in most cases, except understandable waits, like when Atari ANTIC access videoram when you also trying to do that.
Reliability issues in 8bit and in consoles solved very simple ways - first, most where capable to run only one program, and second, console software where extremely reliable, and expensive, much more reliable than business software, sometimes exceeds reliability of military software or mainframe system software.