[bluGill]

You can limit yourself to the performance of a 1mhz 6502 with no OS if you don't like it. Even MSDos on a 8086 with 640K ram allows for things that require complexity of this type (not spin locks, but the tricks needed to make "terminate stay resident" work are evil in a similar way)

[yjftsjthsd-h]

I don't think that's fair. You can go fast, just not more than one task at a time.

[bluGill]

Modern CPUs (since around 2000) go faster in large part because they have multiple cores that can do more than one thing in a time. If your program needs to go faster using more cores is often your best answer and then you will need these tricks. (SIMD or the GPU are also common answers that might or might not be better for your problem)

[yjftsjthsd-h]

Modern CPUs can do 4-5 GHz singled threaded. (Sometimes you can even get a higher clock speed by disabling other cores.) This somewhat outpaces "a 1mhz 6502" even without parallelization.

[bluGill]

They can, but nobody runs a single process on such CPUs. They run some form of OS which implements spinlock, mutexes, and all these other complex things.

I suppose someplace someone is running an embedded system without an OS on such a processor - but I'd expect they are still using extra cores and so have all of the above tricks someplace.

[pjmlp]

I never get the single threaded assertions regarding CPU performance, it is mostly useless in the day of premptive scheduling in modern OSes.

Yes it matters on MS-DOS like OS design, like some embedded deployments and that is about it.

It is even impossible to guarantee a process doesn't get rescheduled into another CPU with the performance impact it entails, unless the process explicitly sets its CPU affinity.

[bluGill]

If you don't allow complev things like spinlocks then all that is left is single thread performance.