On Sun, May 01, 2016 at 09:15:03AM +0100, Chris Wilson wrote:
This effectively reverts
commit afcd950cafea6e27b739fe7772cbbeed37d05b8b Author: Chris Wilson chris@chris-wilson.co.uk Date: Wed Jun 10 15:58:01 2015 +0100
drm: Avoid the double clflush on the last cache line in drm_clflush_virt_range()as we have observed issues with serialisation of the clflush operations on Baytrail+ Atoms with partial updates. Applying the double flush on the last cacheline forces that clflush to be ordered with respect to the previous clflush, and the mfence then protects against prefetches crossing the clflush boundary.
The same issue can be demonstrated in userspace with igt/gem_exec_flush.
Fwiw, longer test cycles still show an issue along the pread/pwrite paths. Not yet convinced if this is the only issue or if it is just paper (though seemingly very pretty paper). -Chris