On Tue, Nov 24, 2015 at 10:13:22PM -0500, Ganesh Ajjanagadde wrote: > This is a trivial rewrite of the loops that results in better > prefetching and associated cache efficiency. Essentially, the problem is > that modern prefetching logic is based on finite state Markov memory, a > reasonable > assumption that is used elsewhere in CPU's in for instance branch > predictors. > > Surrounding loops all iterate forward through the array, making the > predictor think of prefetching in the forward direction, but the > intermediate loop is unnecessarily in the backward direction. > > Speedup is nontrivial. Benchmarks obtained by 10^6 iterations within > solve_lls, with START/STOP_TIMER. File is > tests/data/fate/flac-16-lpc-cholesky.err. > Hardware: x86-64, Haswell, GNU/Linux. > > new: > 17291 decicycles in solve_lls, 2096706 runs, 446 skips > 17255 decicycles in solve_lls, 4193657 runs, 647 skips > 17231 decicycles in solve_lls, 8384997 runs, 3611 skips > 17189 decicycles in solve_lls,16771010 runs, 6206 skips > 17132 decicycles in solve_lls,33544757 runs, 9675 skips > 17092 decicycles in solve_lls,67092404 runs, 16460 skips > 17058 decicycles in solve_lls,134188213 runs, 29515 skips > > old: > 18009 decicycles in solve_lls, 2096665 runs, 487 skips > 17805 decicycles in solve_lls, 4193320 runs, 984 skips > 17779 decicycles in solve_lls, 8386855 runs, 1753 skips > 18289 decicycles in solve_lls,16774280 runs, 2936 skips > 18158 decicycles in solve_lls,33548104 runs, 6328 skips > 18420 decicycles in solve_lls,67091793 runs, 17071 skips > 18310 decicycles in solve_lls,134187219 runs, 30509 skips > > Reviewed-by: Michael Niedermayer <mich...@niedermayer.cc> > Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> > --- > libavutil/lls.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-)
LGTM thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Those who are best at talking, realize last or never when they are wrong.
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