Re: Attempted summary of "RT patch acceptance" thread

["Paul E. McKenney" <paulmck@us.ibm.com>]

On Fri, Jun 10, 2005 at 04:45:38PM -0400, Lee Revell wrote:
> On Fri, 2005-06-10 at 19:37 +0200, Andrea Arcangeli wrote:
> > You don't need to add it to the document, but as a further pratical
> > example of troublesome hardware besides VGA (could be a software issue
> > and not hardware issue though)  
> 
> The VGA problems were due to (X, not kernel!) driver bugs.  Recent
> versions of X are thought to be OK.
> 
> It's the exact same issue described in this paper, scroll down to
> section 4.5.
> 
> http://www.cs.utah.edu/~regehr/papers/hotos7/hotos7.html
> 
> There's absolutely nothing the kernel or PREEMPT_RT can do about this,
> AFAICT even RTAI would be affected, because X lets userspace drivers
> talk directly to the hardware including wedging the PCI bus.

Cute!

I suppose that Eric Piel's approach would avoid this problem if
implemented on a NUMA machine with all processes making use of video
being affinitied to the NUMA node containing the video card.  ;-)

Sounds like I need to add "antisocial hardware" to the list of
things that need to be inspected to validate realtime latencies.

						Thanx, Paul
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