Control Divergence Control divergence occurs when threads in a warp toko Nifforont control flownth hy mokin Nifferent C Time(clocks) ALU1 ALU2 .. ·ALU8 <unconditional ath of an shader code> TT F T FFF P 1f(×>0)( is than X y pow(x,exp); X XX然 y *Ks; X XXXX refl =y Ka; else X然 X X=0; x refl Ka; hs are <resume unconditional Not all ALUs do useful work! shader code> Worst case:1/8 peak performance i ne numper ot ditterent patns can be large when considering nested control flow statements 电子神越女学 010 Control Divergence – Control divergence occurs when threads in a warp take different control flow paths by making different control decisions – Some take the then-path and others take the else-path of an if-statement – Some threads take different number of loop iterations than others – The execution of threads taking different paths are serialized in current GPUs – The control paths taken by the threads in a warp are traversed one at a time until there is no more. – The number of different paths can be large when considering nested control flow statements