On Wed, 2015-06-17 at 14:05 -0700, Jasper St. Pierre wrote: > And yet it's still fast enough. Eliminating roundtrips would be nice, > but we should make sure we're eliminating the roundtrips that matter.
On a 2.3GHz haswell I get about 100k roundtrips per second (measuring with x11perf -pointer). 92 round trips is 0.92 milliseconds. That's twice as long as the vblank interval with CVT-R timing. So unless you're racing the scanline and/or scheduling slow work for the top of the frame, you have about a 2% chance that mapping a window means missing a frame. Maybe mutter gets that right, but I kind of doubt it has that good of an internal cost model. A 2.3GHz haswell is a fast, modern machine. On a 1.7GHz ivybridge I get about 50k/sec. On an SGI Indy you could expect maybe 1.8k/sec; 92 round trips would be 5ms, a third of a frame. Granted not many people make 150MHz MIPS machines these days, but they _are_ making atoms. - ajax _______________________________________________ xorg-devel@lists.x.org: X.Org development Archives: http://lists.x.org/archives/xorg-devel Info: http://lists.x.org/mailman/listinfo/xorg-devel
