> a modern processor is very resilient against losing its functional blocks during operation
I'm very curious, can you elaborate on that?
I'm very curious, can you elaborate on that?
Also x86 has something called “machine check architecture” which constantly monitors the system and the CPU and throws “Machine Check Exceptions” when something goes very wrong.
These exceptions divide into “recoverable” and “unrecoverable” exceptions. An unrecoverable exception generally triggers a kernel panic, and recoverable ones are logged in system logs.
Moreover, a CPU can lose (fry) some caches (e.g.: half of L1), and it’ll boot with whatever available, and report what it can access and address. In some extreme cases, it loses its FPU or vector units, and instead of getting upset, it tries to do the operations at microcode level or with whatever units available. This manifests as extremely low LINPACK numbers. We had a couple of these, but I didn’t run accuracy tests on these specimens, but LINPACK didn’t say anything about the results. Just the performance was very low when compared to normal processors.
Throttling is a normal defense against poor cooling. Above mechanisms try to keep the processor operational in limp mode, so you can diagnose and migrate somehow.
On top of that, I was always interested in high performance / efficient computing and did my M.Sc. and Ph.D. in related subjects.
It's not impossible to gather this knowledge, but it's a lot of rabbit holes which are a bit hard to find sometimes.
You need to know a lot of things to do this. Actually it's half dark art and half science. Vendors do not always tell the full story about their hardware (Intel's infamous AVX frequency, and their compilers' shenanigans when it detects an AMD CPU), and you need to be able to bend the compiler to your will to build the binary the way you want. Lastly, of course, you shall know what you're doing with your code and understand how it translates to assembly and what your target CPU does with all that.
To be able to understand that kind of details, we have valgrind/callgrind, perf, software traces, some vendor specific low-level tools to see what processor is doing, and pure timing-related logging.
Game engines are different beast, I do scientific software, but a friend of mine was doing game engines. Highly optimized graphics drivers are black boxes and that's a whole different game. It's not very well documented, trade secrets ridden, and tons of undocumented behaviors which drivers do to optimize stuff. Plus, you have to use the driver very complex and sometimes ugly ways to make it perform.
While this is hard to start and looks like a big mountain, all this gets way easier when you develop a "feeling for the machine". It's similar how mechanics listen to an engine and say "it's spark plug 3, most probably". You can feel how a program runs and where it chokes just by observing how it runs.
This is why C/C++ is also used in a lot of low level contexts. Yes, it allows you to do some very dangerous things, but if you need to do things fast, and you can prove mathematically that this dangerous thing can't happen, you can unlock some more potential from your system. People doing this is very few, and people who do this recklessly (or just code carelessly) give C/C++ a bad name.
It's not impossible. If Carmack, Unreal, scientific software companies, Pixar, Blender and more are able to do it, you can do it, too.
> To be able to understand that kind of details, we have valgrind/callgrind, perf, software traces, some vendor specific low-level tools to see what processor is doing, and pure timing-related logging.
Working as a data warehouse engineer, I'm not exposed to these kinds of things. Our upstream team, the streaming guys, does have a bit of exposure to performance related to Spark.
> It's similar how mechanics listen to an engine and say "it's spark plug 3, most probably". You can feel how a program runs and where it chokes just by observing how it runs.
> It's not impossible. If Carmack, Unreal, scientific software companies, Pixar, Blender and more are able to do it, you can do it, too.
I kinda feel that I have to switch job to learn this kind of things. I do have some personal projects but they do not need the attention. I'll see what I can do. I have always wanted to move away from data engineering anyway.