On Wednesday 30 April 2014 12:34 PM, Rusty Russell wrote: > 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. > Ok. Will do. Thanks for review With regards Maddy > 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>