diff --git a/site/content/entry/yuzu-fastmem/BENCH_01.png b/site/content/entry/yuzu-fastmem/BENCH_01.png new file mode 100644 index 00000000..4c6973a9 Binary files /dev/null and b/site/content/entry/yuzu-fastmem/BENCH_01.png differ diff --git a/site/content/entry/yuzu-fastmem/BENCH_02.png b/site/content/entry/yuzu-fastmem/BENCH_02.png new file mode 100644 index 00000000..bfe5b06a Binary files /dev/null and b/site/content/entry/yuzu-fastmem/BENCH_02.png differ diff --git a/site/content/entry/yuzu-fastmem/MMU.png b/site/content/entry/yuzu-fastmem/MMU.png new file mode 100644 index 00000000..be8f829f Binary files /dev/null and b/site/content/entry/yuzu-fastmem/MMU.png differ diff --git a/site/content/entry/yuzu-fastmem/SSBU.png b/site/content/entry/yuzu-fastmem/SSBU.png new file mode 100644 index 00000000..9c2da40e Binary files /dev/null and b/site/content/entry/yuzu-fastmem/SSBU.png differ diff --git a/site/content/entry/yuzu-fastmem/banner.png b/site/content/entry/yuzu-fastmem/banner.png new file mode 100644 index 00000000..5722698f Binary files /dev/null and b/site/content/entry/yuzu-fastmem/banner.png differ diff --git a/site/content/entry/yuzu-fastmem/index.md b/site/content/entry/yuzu-fastmem/index.md new file mode 100644 index 00000000..183ad9fa --- /dev/null +++ b/site/content/entry/yuzu-fastmem/index.md @@ -0,0 +1,119 @@ ++++ +date = "2021-06-08T04:00:00+05:30" +title = "New Feature Release - Fastmem Support" +author = "CaptV0rt3x" +forum = 415882 ++++ + +Hey there, yuz-ers! +While all of you wait eagerly for the release of Project Hades, our shader decompiler rewrite, we thought we'd bring you a nice little surprise to keep you occupied. +We present to you, the newest addition to yuzu's ever-improving features list - Fastmem (Fast Memory Access)! + + +  + +This is now available in the latest yuzu Early Access build (1759 or newer) and we intend to make this available in Mainline builds very soon. +As always, we ask that you test various games with these builds and if you encounter any issues, bugs, or crashes, please reach out to us via the [Discord](https://discord.gg/u77vRWY) Patreon channels. + +**Note: This feature is enabled by default.** + +## What is Fastmem? + +Fastmem or Fast Memory Access, is a well-known feature among emulator developers and emulation enthusiasts. +Emulators like [Dolphin](https://dolphin-emu.org/) and [Citra Android](https://citra-emu.org/) have implemented this in the past. + +All modern Operating Systems have this concept of "virtual memory," where addressable memory (from the running process) is a space of memory addresses that are only "known" to that process, e.g. Discord on your PC, or Super Mario Odyssey on your Switch — and the addresses are translated by the Switch's MMU (Memory Management Unit) to the physical location in the Switch’s physical RAM as the game runs. + +  + +{{< imgs + "./MMU.png|Illustration of an MMU (By Mdjango, Andrew S. Tanenbaum)" +>}} + +In yuzu, we emulate the Switch's virtual address space for the running process. +But, that means for each time the game tries to read/write memory, which happens millions of times per frame, we need to basically "decode" where that Switch virtual address maps to our "emulated" Switch memory (RAM allocated for yuzu). +This adds a lot of overhead when you consider how much the game reads/writes to memory. + +The idea behind Fastmem here is to map the emulated Switch game's addressable memory on the host (Windows / Linux), at offset addresses. +The offset is a constant. + +## The Technical - HOW? + +On the Switch, we have 4GB of memory. +The hardware supports a virtual memory size of 48bits (just like x64); however, the Switch kernel limits this to only 39bit to save some memory for storing page tables. +This results in a 512GB virtual address space (2^39) for use. (A page table is the data structure used to store the mapping between virtual addresses and physical addresses.) + +To emulate this, we allocated a HUGE page table, which had an offset for each memory page addressable in the virtual memory region of the Switch. This table alone was 1GB in size! +And whenever a game wanted to access the memory, we looked up this table, which resulted in roughly ~10 x64 CPU instructions and twice the memory latency. +That latency being: first read the table's value, then read the correct memory. + +Fastmem, however, uses the host MMU to rebuild the same 39bit virtual memory arena. +Here, we're lucky that Nintendo limits the memory to 39bit. +We cannot allocate 48bit because that's the entire virtual address space on the host. + +This cuts the effort to access the memory down to 3+1 x64 CPU instructions with a single memory latency. +3 instructions to check if the pointer is smaller than 39 bit, and one memory load instruction. +We need this size check to ensure out-of-bounds memory access won't return any physical address. + + +## The Challenges + +Implementing Fastmem required two major things in [Dynarmic](https://github.com/MerryMage/dynarmic/), our JIT recompiler. + +**First:** A64 Fastmem support on Dynarmic. + +Dynarmic has had support for A32 Fastmem (see Citra Android) for a while now. +A64 Fastmem support was [originally worked on a year ago by MerryMage and vdwjeremy](https://github.com/MerryMage/dynarmic/pull/528) but it never got merged to the master branch. + +[degasus](https://github.com/degasus/) worked with [MerryMage](https://github.com/MerryMage/) to clean up and get [these changes merged](https://github.com/MerryMage/dynarmic/pull/613) to the master branch so that yuzu could benefit from this. + +**Second:** To generate the 512GB virtual address space with the same mappings as on the Switch. + +degasus proved last year that this was easy to implement on Linux as the POSIX mmap call provided very similar features to the Horizon OS. +But it was a huge challenge for Windows, as the Windows Virtual Memory API is larger with a few missing features. +Moreover, while Windows page tables were 4K aligned, Windows memory management was 64K aligned for [outdated reasons](https://devblogs.microsoft.com/oldnewthing/20031008-00/?p=42223). + + +## The Solutions + +Turns out, Microsoft had realized this too and frequently patched their Virtual Memory API. +With the release of Windows 10 v1803, their new API supported new "placeholder" memory which didn't suffer from the previous limitations. + +Thanks to [Breadfish64](https://github.com/BreadFish64/), who used this new API in their Gameboy emulator and showed us that it was now indeed possible to support Fastmem on Windows. +Unfortunately, this makes the feature usable only on Windows versions 1803 and higher. + +Since we already met the base requirements for our new Fastmem implementation long ago, our devs were able to quickly address the missing pieces. +[bunnei](https://github.com/bunnei/) implemented the much-needed kernel rework changes in yuzu, degasus cleaned up their original proof-of-concept code for Linux, and [Rodrigo](https://github.com/ReinUsesLisp/) implemented the Windows Fastmem support. +[Blinkhawk](https://github.com/FernandoS27) provided valuable advice and coordinated these efforts to get the feature release-ready. + +## The Results + +As an added bonus, game booting/loading times have been improved thanks to these changes. +Thanks to developer Rodrigo, Normal GPU accuracy no longer triggers a myriad of exceptions on the Smash character selection screen, improving its performance from 10-20 FPS to a full 60. + +  +{{< imgs + "./SSBU.png|Super Smash Bros. Ultimate" +>}} + +For all game benchmarks, we utilized a PC built to our own recommended hardware spec. +In this testing we observed performance improvements ranging from 15-60% in some of the most demanding areas of gameplay. +Please note the marked titles that were tested with the processor limited to 2.4Ghz, to synthetically make it slower than usual and highlight the improvements. + +  +{{< imgs + "./BENCH_01.png|The * indicates titles tested at 2.4Ghz" +>}} + +  +{{< imgs + "./BENCH_02.png|The * indicates titles tested at 2.4Ghz" +>}} + +##### That's all we have for now, see you soon with exciting news about Project Hades and more! Happy emulating! + +  +

+Please consider supporting us on [Patreon](https://www.patreon.com/yuzuteam)!
+If you would like to contribute to this project, check out our [GitHub](https://github.com/yuzu-emu/yuzu)! +

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