Ingo Molnar <mingo@xxxxxxxxxx> writes: > * Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx> wrote: > >> Performance data for different FAULT_AROUND_ORDER values from 4 socket >> Power7 system (128 Threads and 128GB memory). perf stat with repeat of 5 >> is used to get the stddev values. Test ran in v3.14 kernel (Baseline) and >> v3.15-rc1 for different fault around order values. >> >> FAULT_AROUND_ORDER Baseline 1 3 4 5 8 >> >> Linux build (make -j64) >> minor-faults 47,437,359 35,279,286 25,425,347 23,461,275 22,002,189 21,435,836 >> times in seconds 347.302528420 344.061588460 340.974022391 348.193508116 348.673900158 350.986543618 >> stddev for time ( +- 1.50% ) ( +- 0.73% ) ( +- 1.13% ) ( +- 1.01% ) ( +- 1.89% ) ( +- 1.55% ) >> %chg time to baseline -0.9% -1.8% 0.2% 0.39% 1.06% > > Probably too noisy. A little, but 3 still looks like the winner. >> Linux rebuild (make -j64) >> minor-faults 941,552 718,319 486,625 440,124 410,510 397,416 >> times in seconds 30.569834718 31.219637539 31.319370649 31.434285472 31.972367174 31.443043580 >> stddev for time ( +- 1.07% ) ( +- 0.13% ) ( +- 0.43% ) ( +- 0.18% ) ( +- 0.95% ) ( +- 0.58% ) >> %chg time to baseline 2.1% 2.4% 2.8% 4.58% 2.85% > > Here it looks like a speedup. Optimal value: 5+. No, lower time is better. Baseline (no faultaround) wins. etc. It's not a huge surprise that a 64k page arch wants a smaller value than a 4k system. But I agree: I don't see much upside for FAO > 0, but I do see downside. Most extreme results: Order 1: 2% loss on recompile. 10% win 4% loss on seq. 9% loss random. Order 3: 2% loss on recompile. 6% win 5% loss on seq. 14% loss on random. Order 4: 2.8% loss on recompile. 10% win 7% loss on seq. 9% loss on random. > I'm starting to suspect that maybe workloads ought to be given a > choice in this matter, via madvise() or such. I really don't think they'll be able to use it; it'll change far too much with machine and kernel updates. I think we should apply patch #1 (with fixes) to make it a variable, then set it to 0 for PPC. Cheers, Rusty. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>