On 04/10/2013 05:22 PM, Michael Wang wrote: > Hi, Peter > > Thanks for your reply :) > > On 04/10/2013 04:51 PM, Peter Zijlstra wrote: >> On Wed, 2013-04-10 at 11:30 +0800, Michael Wang wrote: >>> | 15 GB | 32 | 35918 | | 37632 | +4.77% | 47923 | +33.42% | >>> 52241 | +45.45% >> >> So I don't get this... is wake_affine() once every milisecond _that_ >> expensive? >> >> Seeing we get a 45%!! improvement out of once every 100ms that would >> mean we're like spending 1/3rd of our time in wake_affine()? that's >> preposterous. So what's happening? > > Not all the regression was caused by overhead, adopt curr_cpu not > prev_cpu for select_idle_sibling() is a more important reason for the > regression of pgbench. > > In other word, for pgbench, we waste time in wake_affine() and make the > wrong decision at most of the time, the previously patch show > wake_affine() do pull unrelated tasks together, that's good if current > cpu still cached hot data for wakee, but that's not the case of the > workload like pgbench.
Please let me know if I failed to express my thought clearly. I know it's hard to figure out why throttle could bring so many benefit, since the wake-affine stuff is a black box with too many unmeasurable factors, but that's actually the reason why we finally figure out this throttle idea, not the approach like wakeup-buddy, although both of them help to stop the regression. It's fortunate that there is a benchmark could help to find out the regression, and now we have a simple and efficient approach ready for action ;-) Regards, Michael Wang > > The workload just don't satisfied the decision changed by wake-affine, > the more wake-affine active, the more it suffered, that's why 100ms show > better results than 1ms, but when reached some rate, the benefit and > lost of wake-affine will be balanced. > > Regards, > Michael Wang > >> >> >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
