On: Ratification of the RISC-V Base ISA and Privileged...

[snvzz]

While I haven't looked hard into it, I hope they didn't throw in assumptions that affect context switch speed, particularly on pure microkernel multiserver systems that depend on it and are used in critical applications that require high assurance and low, bounded IPC and interrupt response times.

[DSingularity → snvzz]

What are examples of such systems?

[monocasa → DSingularity]

The l4 variants don't even clear all the registers on an fast path IPC.

[harry8 → DSingularity]

There are none of any practical use, but we live in hope.

[p_l → harry8]

If you use a phone with a Qualcomm modem you use one such system, based on OKL4 (or at least they used to use OKL4 + L4 Linux for non hard RT parts)

[harry8 → p_l]

Not a multi-server operating system. Source: worked on it.

Unless it changed, L4 is used with additional code co-located as the base-band modem on its own cpu. Small RTOS is not a multi-server micro-kernel based os.

[p_l → harry8]

I suspect we might be using different meanings of multi-server microkernel OS, unless the modem software is even more limited than I thought - I meant that the system is composed of multiple communicating servers. Does the modem just have few independent colocated "big" servers (like the ancient 4.2 BSD server for Mach)?

EDIT: Also, had some fun in the past learning about the modem software on Qualcomm modems, back before iPhone or Android so nice to meet someone who worked on it :)

[panpanna → harry8]

ARM removed similar & related functions in v8 since it messes up exception handling in a deep pipeline.

IIRC Linux stopped using this long ago as the performance improvement was not worth the extra code (although Linux is not as heavy on ipc as l4 & co)