Re: task switching at Page Faults

From: Helge Hafting
Date: Tue Apr 20 2004 - 03:16:14 EST

Fabiano Ramos wrote:
Hi all.

I am in doubt about the linux kernel behaviour is this situation:
supose a have the process A, with the highest realtime
priority and SCHED_FIFO policy. The process then issues a syscall,
say read():

1) Can I be sure that there will be no process switch during the
syscall processing, even if the system call causes a page fault?

A page fault means your realtime process must wait, because the
data it wants isn't available yet. (Data have to be fetched
from disk/device which takes lots of time.)

There is nothing wrong with handing the cpu to some other
lower priority process unser such circumstances, because your realtime
process are stuck and can't use it anyway.

The realtime process wil grab the cpu as soon as it gets ready to run anyway,
I believe the scheduler looks for this sort of thing when the pagefault
eventually completes.

Helge Hafting

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