qemu VS QEMU

https://gitlab.com/qemu-project/qemu/-/blob/master/hw/scsi/s...

QEMU's IOThreads allow the user to configure the threads and get something similar to thread per core architecture. But if 1 thread becomes a bottleneck, then some form of thread synchronization is needed again even with thread per core architecture. Some problems can be parallelized and they work well with thread per core.

Add `ENV ERL_FLAGS="+JPperf true"` to your Dockerfile and it will build just fine cross platform. The flag just changes some things during build time and won’t affect runtime performance.

[1] https://gitlab.com/qemu-project/qemu/-/issues/1034

> I don't know how rdcycle works on qemu.

That's a good question! I had to look it up myself ...

Obviously qemu TCG isn't a cycle-accurate emulation. Using RDCYCLE / reading the corresponding CSR eventually calls https://gitlab.com/qemu-project/qemu/-/blob/69680740eafa1838... which calls cpu_get_host_ticks is basically an arch-independent wrapper around RDTSC.

So it just measures the time taken to run using RDTSC. Which I guess is what you would want (maybe?). It would measure the time taken to emulate the vector instruction in host instructions.

> This benchmark is more meant for developers to figure out how to vectorize algorithms effectively, as in which instructions to choose.

Absolutely, I'm not saying the qemu results would say anything very deep, but they're kind of interesting from the point of view of either optimizing qemu or if you have to use qemu because the hardware you want isn't available / isn't cheap enough.

I see the commits that started switch support from RVV 071 to 100 start here, https://gitlab.com/qemu-project/qemu/-/commit/9ec6622db30df1c00d863c1ffc33341f9e0a534d

>> https://gitlab.com/qemu-project/qemu/-/issues/1696 ]

> Can I please just get the detail in mail instead of having to go look at random websites?

Maybe it's me but if I did boot boot linux 292.612 times to find a bug, you might as well click a link to a repository of a major open source project on a major git hosting service.

Is it really that weird to ask people online to check a website? Maybe I don't know the etiquette of these mail lists so this is a geniune question.

Capstone is used[1] by QEMU as disassembly engine in debug logs and in monitor mode debugger, by the way, so it's in the scope of the RISE effort.

[1] https://gitlab.com/qemu-project/qemu/-/blob/master/disas/cap...

A user on the qemu bugtracker found a way to get the Intel Arc working across resets without crashing the host: Just don't passthrough the audio device of the GPU and everything works!

[1]https://gitlab.com/qemu-project/qemu/-/commit/3412d8ec9810b819f8b79e8e0c6b87217c876e32 [2]https://gitlab.com/alex.williamson/qemu/-/commit/9a6d1822a2bd55f5dee1aec1b6529ae57949d5ba.patch

My most-wanted QEMU feature: https://github.com/qemu/qemu/commit/a2260983c6553

Using `gic-version=3` on macOS you can now use more than 8 cores on ARM chips.

A better solution is just to write a plain ass shell script that tests if various C snippets compile.

https://github.com/oilshell/oil/blob/master/configure

https://github.com/oilshell/oil/blob/master/build/detect-pwe...

Not an unholy mix of m4, shell, and C, all in the same file.

---

These are the same style as a the configure scripts that Fabrice Bellard wrote for tcc and QEMU.

They are plain ass shell scripts, because he actually understands the code he writes.

https://github.com/qemu/qemu/blob/master/configure

https://github.com/TinyCC/tinycc/blob/mob/configure

OCaml’s configure script is also “normal”.

You don’t have to copy and paste thousands of lines of GNU stuff that you don’t understand.

(copy of lobste.rs comment)

Related:

A fast Pascal (Delphi) WebAssembly interpreter:

https://github.com/marat1961/wasm

WASM-4:

https://github.com/aduros/wasm4

Curated list of awesome things regarding WebAssembly (wasm) ecosystem:

https://github.com/mbasso/awesome-wasm

Also, it would be nice if there was a WASM (soft) CPU for QEMU, which (if it existed!) would go here:

https://github.com/qemu/qemu/tree/master/target

> architectural registers are always updated

In tiny code, the guest registers (global TCG variables) are stored in the host's registers until you either call an helper which can access the CPU state or you return (`git grep la_global_sync`). This is the reason why QEMU is not so terribly slow.

But after a check, this also happens when you access the guest memory address space! https://github.com/qemu/qemu/blob/master/include/tcg/tcg-opc... (TCG_OPF_SIDE_EFFECTS is what matters)

But still, in the end, it's the same problem. What QEMU does, can be done in LLVM too. You could probably be more efficient in LLVM by using the exception handling mechanism (invoke and friends) to only serialize back to memory when there's an actual exception, at the cost of higher register pressure. More or less what we do here: https://rev.ng/downloads/bar-2019-paper.pdf

Um, in case you don't know, UTM (based on QEMU) is out for quite a while.

Some of these tools include Oracle VM VirtualBox (that I've used since before the acquisition of Sun Microsystems by Oracle), VMWare Workstation Player, and QEMU, but last year, I found out about Multipass.

For C/C++ projects that use meson as the build system, there is an excellent way to manage dependencies:

https://mesonbuild.com/Wrapdb-projects.html

https://mesonbuild.com/Wrap-dependency-system-manual.html

meson will download and build the libraries automatically and give you a variable which you pass as a regular dependency into the built target:

https://github.com/qemu/qemu/tree/005ad32358f12fe9313a4a0191...

https://github.com/harfbuzz/harfbuzz/tree/main/subprojects

https://github.com/harfbuzz/harfbuzz/blob/37457412b3212463c5...

Or, if you're using proper operating systems, they're managed by the usual package manager, just like everything else.

For all the users of the Linux platform, QEMU is the VM that you should go for. This software comes without any price tag and works as an emulator of various machines with utmost ease and completion; the software uses dynamic translations to emulate hardware peripherals and enhances its overall performance. If you are using QEMU as a virtualizer, then it will function exactly like the host system (provided you have the right set of hardware).

In this tutorial, we set up macOS and Windows virtual machines on UTM, a macOS application that provides a GUI wrapper for QEMU, a powerful open-source emulator and virtualizer. UTM allows you to easily manage and run virtual machines without memorizing complex commands. It also has special handling for macOS, making it simpler to install compared to other virtual machine software.