On 10/31/07, Thomas Hellström <[EMAIL PROTECTED]> wrote: > Dave Airlie wrote: > > On 10/31/07, Thomas Hellström <[EMAIL PROTECTED]> wrote: > > > >> Dave, > >> > >> When starting out with TTM i did look a little at AGP caching issues and > >> there was an issue with cached memory and speculative pre-fetching that > >> may affect the mapped-cached memory, > >> and that we need to know about but perhaps ignore. > >> > >> Suppose you bind a page to the AGP aperture, but don't change the kernel > >> linear map caching policy. > >> Then a speculatively prefetching processor may read the memory into its > >> cache and then decide it doesn't > >> want to use it, and actually write it back. > >> Meanwhile the GPU may have changed the contents of the page and that > >> change will be overwritten. Apparently there were big problems with AMD > >> Athlons actually doing this. Linux people claiming it was an Athlon bug > >> and AMD people claiming it was within specs. > >> > >> > > > > http://www.linuxjournal.com/files/linuxjournal.com/linuxjournal/articles/061/6148/6148s1.html > > > > Is what I believe you are talking about, I'll add something to the > > comment mentioning this.. > > > > > Yup. In the end I believe the "change_page_attr(), global_flush_tlb()" > sequence was the final outcome of this, but as I understand it, > with your new code we never write through the GTT, which makes the only > possible problem overwrites of GPU written data. >
Well so far we've only dealt with Intel CPU/GPU combinations which hopefully don't suffer from this issue.. I'll put a comment in but tbh there are lots of ways to mess up things with the current APIs.. Try allocating a snooped batchbuffer, or a snooped private back buffer or anything involved in a blit.... I'm going to add checks for some of the more stupid things in the Intel superioctl code... Dave. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
