Re: Attempted summary of "RT patch acceptance" thread

[Andrea Arcangeli]

On Fri, Jun 10, 2005 at 04:45:38PM -0400, Lee Revell wrote:
> AFAICT even RTAI would be affected, because X lets userspace drivers
> talk directly to the hardware including wedging the PCI bus.

Yes, I made the usb example exactly to show how latency bugs can be
longstanding in the kernel too without requiring X or hardware bugs
(this usb thing breaks kernel latency for years and yet nobody fixed it
simply because it just works fine in practice, I noticed because
apparently my PIT or tsc goes out of sync over time, and in turn my
system time was going into the future pretty quick with HZ=1000, or I
would have never noticed, of course I'm compiling the kernel with HZ=100
on that system to work around it). Those latency issues can showup in
random drivers all the time, and this one was of an extreme magnitude in
the millisecond range. The smaller the magnitude of the latency impact,
the more frequently you should find it in drivers.
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