New Release of MINIX 3 For x86 and ARM Is NetBSD Compatible

An anonymous reader writes MINIX 3 is a small POSIX-compliant operating system aimed at high reliability (embedded) applications. A major new version of MINIX 3 (3.3.0) is now available for download at www.minix3.org. In addition to the x86, the ARM Cortex A8 is now supported, with ports to the BeagleBoard and BeagleBones available. Finally, the entire userland has been redone in 3.3.0 to make it NetBSD compatible, with thousands of NetBSD packages available out of the box. MINIX 3 is based on a tiny (13 KLoC) microkernel with the operating system running as a set of protected user-mode processes. Each device driver is also a separate process. If a driver fails, it is automatically and transparently restarted without rebooting and without applications even noticing, making the system self-healing. The full announcement, with links to the release notes and notes on installation, can be found at the Minix Google Groups page.

Comments

Re:Drivers as processes?

[bluefoxlucid]

The file system write or read request doesn't return anything, the driver is detected as dead (heartbeat?), it's killed, resurrected, journals are replayed, and the request is resubmitted to the FS driver.

It'll work. The program might notice a small pause, as if the disk was busy or the kernel yielded schedule to an interrupt handler.

Re:Linux clone

[bluefoxlucid]

From what I've seen, Minix is fast. It's built for speed, avoiding many costs of IPC the same way Linux does.

In Linux, the address space is split. IA-32 4G/4G causes a full TLB and cache flush at syscall entry and return, creating massive slowness. IA-32 normal 3G/1G operation puts 1G at the top for kernel mappings and 3G at the bottom, while x86-64 puts 128TB at the top and 128TB at the bottom. In both cases for split address space, there's no TLB or cache flush when syscalling into the kernel; and returning to user space requires only selective cache and TLB invalidation, removing kernel-private data and leaving userspace data in tact. This greatly improves cache utilization and reduces expensive pagefaults by completely avoiding the kernel/user context switch, replacing it with a simple mode switch.

In Minix, the many kernel contexts make all the same mappings, but lock access to the specific service. It's the same as Linux's split mapping, but with parts of the kernel unable to access other parts; IPC involves a few TLB and cache invalidations in each direction. This strategy lets you run an entire round trip call in under 100nS. It's about as long each way as a CALL and RET, so it's about the overhead of adding a function call along the code path.

Re:Does Minix have much real-time capability?

[SkOink]

VxWorks?

VxWorks is a great product. It's also waaaayyy outside of the price range of a hobbyist developer. Getting up and running with the VxWorks suite of tools can easily cost 20k (USD), and the recurring license fees are pretty significant as well. I would also bet that auditing the VxWorks source code (or trying to get custom patches in) would cost significantly more.

Re:Linux clone

[bluefoxlucid]

It has a 2% to 4% penalty for IPC, specifically. This is like when Theo de Raadt chose to argue with me that position-independent executables were "very expensive" and had "high performance overhead," and I pulled out oprofile and found that 0.2% of the execution time occurred in the main executable--which was 6% slower (when including -fomit-frame-pointer no longer providing a 5% boost), giving a total overhead of 0.012% total system slowdown--a few seconds lost per day.

The difference is I was doing that back then, and not referencing shit I did 10 years ago.

Minix's overhead is small. Minix uses fixed-length buffers, zero-copy strategies, mode switching, and the like to avoid doing any real work for IPC. It's like adding a function call to your code paths--like if you called get_fs_handle() and it called __real_get_fs_handle() without inlining it.