Comment 7 for bug 541511

Created an attachment (id=34247)
new gtt cache coherency patch

New version of my patch. Changes:
- improved cache coherency checker. Instead of always using the same address it now constantly changes. Should increase the chance of catching an inconsistency. But still, this won't catch everything and there's still the chance that the gpu reads crap and dies before we detect that the chipset flush doesn't work.

- increased the size of the magic gtt write. I don't like this, but it seems to help. Given that testing of the last patch showed that I've only implemented a fancy delay I've tried different techniques. Unfortunately none worked.

Testing feedback highly welcome. I've you report results, please add some details about your machine: Processor (model and frequency), ram (type, speed & size). Perhaps there's a pattern there.

Oh, and legolas created a nice small script that calculates the cache failure rate of the running kernel:

https://bugs.freedesktop.org/attachment.cgi?id=34240