Summary: Does Linux Do Multitasking at Kernel Level

[Sudheesh Krishnankutty <sudheesh@softjin.com>]

Dear Linuxmanagers,

Thanks to

Jonas Bofjall j-linman@gazonk.org
Davin S George davin@kiwifokes.com
Ravi - ravi.channavajhala@csfb.com
Matt Welsh - mdw@cs.berkeley.edu
Julian Hall - jules@acris.co.uk
Jeffrey Taylor - jeff.taylor@ieee.org
Brett Geer - Gbrett@brabys.co.za

Here is the summary for my question.

----- Matt Welsh Wrote --------
Yes, it does.

On an SMP system multiple threads can be executing within the kernel at
one time, so the kernel has fine-grained locks within it. Kernel code is
generally not preempted except by hardware interrupts - and on return
from an interrupt the original kernel code executes, not the process
scheduler.

However, very recently a "preemptible kernel patch" was announced which
effectively made the Linux kernel preemptible in the way that you
describe. I don't know the details but it is not available and might be
part of the 2.5 development series - a Google search will probably turn
it up.

----- ravi wrote------------

Pre-emptive kernel threading is not supported in 2.4 kernel.
You have to wait for 2.5 for that.

As for kernel multitasking, Linux kernel is fully reentrant,
since the time immemorial.

-----brett wrote ------

the kernel itself cannot be preempted, however new patches for a pre-emptable kernel
just made it into the 2.5 kernel and exist for the 2.4 series

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