On Mon, Feb 27, 2012 at 05:10:24PM +0000, Chris Wilson wrote: > On Mon, 27 Feb 2012 17:30:19 +0100, Daniel Vetter <daniel at ffwll.ch> wrote: > > On Fri, Feb 24, 2012 at 09:21:51PM +0000, Chris Wilson wrote: > > > Doing mixed rendering into the front/back scanout buffers lead to the > > > interesting rediscovery of clflushing when page-flipping. A painful > > > experience indeed. > > > > > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk> > > > > Hm, I might be a bit dense here (again ...) but I don't follow what this > > exactly fixes. Care to elaborate a bit? > > When we are page-flipping, we take an active render buffer and flush it > to the display plane. This involves a migration into the uncached > domain and a clflush. If we allow the bo to transistion back to LLC > cached for fast rendering when it becomes the back-buffer again, we > incur another clflush back into the display place, even though we never > touch it with the CPU whilst it is in the CPU domain. Similarly, if we > are recycling bo used else for render buffers to be page-flipped. The > patch avoids the defensive clflush by recording when we ignore transitions > in and out of the CPU cache domain due to cache coherency and replaying > those missed clflushes when the object is no longer cache coherent. > > The effect of the extra clflushes is quite pronounced (>30% framerate > drop for glxgears) and really does interfere with experiments to manage > cache levels. It's not the only bottleneck, but it is the major one. Ah, so you're playing around and have fun ;-) I think I'll wait with picking this up until you come up with the real deal ... -Daniel -- Daniel Vetter Mail: daniel at ffwll.ch Mobile: +41 (0)79 365 57 48
