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SubjectRe: Linux Kernel constraints!
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.
> 2. kernel is not reentrant. ie.only one thread in kernel context at a time.
> 3. kernel is not multi processing in the sense that on multiprocessor
> systems it will run on only one cpu at a time.
>
> will somebody can clarify these doubts and version which enabled it to be
> otherwise.

The first one is true, and since they all mean the same thing, they all
are :)

At least, that's the case in 2.0.x. 2.1 (and soon 2.2) have improved
matters a fair bit as some of the "easier" targets - VM, signal-handling,
process handling - have finer grained locks around them.

However the filesystem and network stuff is still pretty single-threaded,
although this will change in time, too.

The funny thing is it's not such an issue with Linux because it has such
low latencies that it still scales better than NT on 4 way boxes.

Matthew.
- now concerned that the NT people have finalyl found some (exaggerated)
FUD that's true :)


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