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SubjectRe: Linux Kernel constraints!


On Thu, 21 Jan 1999, Oliver Xymoron wrote:

> On Thu, 21 Jan 1999, Yogesh Bansal wrote:
>
> > Recently(dec.) in WindowsNT magazine comparisons/similarities between
> > various flavours of unix and nt had come. In the same article Linux was
> > ignored as enterprise os on account of following kernel 'limitations' :
> >
> > 1. kernel is not preemptive. ie even a higher priority user thread cant
> > cause another thread to be swapped if the other thread is presently running
> > in privileged/kernel context.
>
> Not true. All things that are not running with interrupts disabled can be
> preempted.

by bottom half. Looks like the author means hard RT stuff.

> > 3. kernel is not multi processing in the sense that on multiprocessor
> > systems it will run on only one cpu at a time.
>
> And this is even more absurd. SMP is _symmetric_. Kernel runs on all
> processors _by definition_. There may be some confusion here with respect
> to lock granularity though. The very first SMP kernels had a single lock
> that protected most data structures, which drastically limited kernel
> concurrency. Current kernels have more fine-grained locking that allow
> much better concurrency and therefore better scaling.

kernel_lock is still there. It's held by all filesystem-related
syscalls. dcache is still not SMP-safe. Ditto for struct file -related
operations.


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