Re: RT; RH 6.0

Adrian Godwin wrote:

> From: Adrian Godwin <adrian@...>
>
>
> > From: Brian Bartholomew <bb@...>
> > Subject: Re: BDI install disk for EMC
>
> > So far I count 15 people who have expressed interest in purchasing a
>
> > "Brain-Dead Install" EMC cd based upon some version of Red Hat, were
>
> > it offered. I agree that a version for Red Hat 6.1 would be a lot
> > more interesting than for 5.2, if the kernel work were feasible.
>
> The RTLinux website seems to have a set of patches for the 2.2
> kernel series : it's possible that the effort to integrate into
> Redhat 6.1 won't be that large. These patches are against a stock
> kernel rather than a redhat kernel, I think, but I don't have any
> problem in running a stock kernel in a redhat 6.0 system.

I think there are two issues with this. One is that, last time I
looked, the
real time patches did not save the state of the floating point hardware,
and
so the RT patches have to be patched to save and restore FP state as
well,
on a task switch.

Then, there is a new issue, that something changed in the get time of
day
system call, that made it take a very long time to return the result.
This
is apparently called every time the RT module completes, to schedule
the next call of the RT module in EMC. This is not exactly an issue
with the RT patch, but it caused a performance problem in EMC.
One of the fixes was to go to a recurring interrupt rather than
rescheduling
the interrupt each time. (This makes more sense, anyway, when you
are talking about periodic interrupst at KHz rates.)

Jon