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

Bakul Shah bakul at iitbombay.org
Thu Dec 15 15:36:12 AEST 2022


Don't see how unless they put multiple related services in the same
address space, which reduces context switching but tends toward a
monokernel (& increased coupling). Unless I am misunderstanding you.

> On Dec 14, 2022, at 6:54 PM, Larry McVoy <lm at mcvoy.com> wrote:
> 
> 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....
> 
> -- 
> ---
> Larry McVoy           Retired to fishing          http://www.mcvoy.com/lm/boat



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