Re: a joint letter on low latency and Linux

[David Schleef]

On Thu, Jun 29, 2000 at 10:31:07PM -0600, Richard Gooch wrote:
> 
> I don't see why the MM stuff is an issue: just tap in at every place
> where we do a user<->kernel transition. There's not that many, after
> all.
> 
> So if a hard-RT user-space process suddenly takes a page fault, the
> CPU switches to kernel mode (still running under the RTLinux
> scheduler), and the first thing we do is call rtl_drop_rt(). Same for
> all other kernel entry points.
> 

This is, in fact, exactly what RTAI/LXRT is planning to do.  (Actually,
"does", if you count my current source tree.)  Except that you get to
chose whether to drop priority and execute the trap, kill the process,
or have the system call fail.  (If it is a system call that trapped --
eventually, we'll implement a few important system calls, like
sys_gettimeofday().)

dave...