[TUHS] Clever code (was Re: Re: Stdin Redirect in Cu History/Alternatives?

[Larry McVoy]

Wasn't there some statement that QNX dropped some of these?  Copy plus
context switch?

On Wed, Dec 14, 2022 at 04:29:45PM -0800, Bakul Shah wrote:
> On Dec 11, 2022, at 7:09 PM, Andrew Warkentin <andreww591 at gmail.com> wrote:
> > 
> > It's not necessarily true that microkernels are significantly slower.
> 
> uKernels are usually quite fast as they do so little. What can be slow
> is emulating a Unix like OS on top due to context switches. For instance,
> a user process doing read() will have the following context switches:
> 
>   userProc->uK->FileSystem->uK->diskDriver->uk->FileSysem->uK->userProc
> 
> or worse (I didn't account for a few things). Because of this even some
> uKernels run a few critical services + drivers in the supervisor mode.
> But overall slowdown of such a unix emulation will very much depend on the
> workload and also what kind of performance improvements you are willing to
> try in a complex kernel vs same services running in user mode.
> 
> At present the linux kernel has about 31+ Million lines (accounting for
> all architectures, filesystems, device drivers etc.). The FreeBSD 13.x
> kernel is about 8.7M LoC (of which 44-45% are in device drivers). I only
> counted .c and .h files. In contract FreeBSD 2.2.2 kernel has ~554K LoC.
> This LoC growth is entirely understandable but I wonder how things may
> have turned out in an alternate universe of uKernel based designs....

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Larry McVoy           Retired to fishing          http://www.mcvoy.com/lm/boat