* Vaidyanathan Srinivasan <svaidy@xxxxxxxxxxxxxxxxxx> wrote: > * Ingo Molnar <mingo@xxxxxxx> [2009-03-04 18:33:21]: > > > > > * Arun R Bharadwaj <arun@xxxxxxxxxxxxxxxxxx> wrote: > > > > > $taskset -c 4,5,6,7 make -j4 > > > > > > my_driver queuing timers continuously on CPU 10. > > > > > > idle load balancer currently on CPU 15 > > > > > > > > > Case1: Without timer migration Case2: With timer migration > > > > > > -------------------- -------------------- > > > | Core | LOC Count | | Core | LOC Count | > > > | 4 | 2504 | | 4 | 2503 | > > > | 5 | 2502 | | 5 | 2503 | > > > | 6 | 2502 | | 6 | 2502 | > > > | 7 | 2498 | | 7 | 2500 | > > > | 10 | 2501 | | 10 | 35 | > > > | 15 | 2501 | | 15 | 2501 | > > > -------------------- -------------------- > > > > > > --------------------- -------------------- > > > | Core | Sleep time | | Core | Sleep time | > > > | 4 | 0.47168 | | 4 | 0.49601 | > > > | 5 | 0.44301 | | 5 | 0.37153 | > > > | 6 | 0.38979 | | 6 | 0.51286 | > > > | 7 | 0.42829 | | 7 | 0.49635 | > > > | 10 | 9.86652 | | 10 | 10.04216 | > > > | 15 | 0.43048 | | 15 | 0.49056 | > > > --------------------- --------------------- > > > > > > Here, all the timers queued by the driver on CPU10 are moved to CPU15, > > > which is the idle load balancer. > > > > The numbers with this automatic method based on the ilb-cpu look > > pretty convincing. Is this what you expected it to be? > > Yes Ingo, this is the expected results and looks pretty good. However > there are two parameters controlled in this experiment: > > 1) The system is moderately loaded with kernbench so that there are > some busy CPUs and some idle cpus, and the no_hz mask is does not > change often. This leads to stable ilb-cpu selection. If the > system is either completely idle or loaded too little leading to > ilb nominations, then timers keep following the ilb cpu and it is > very difficult to experimentally observe the benefits. > > Even if the ilb bounces, consolidating timers should increase > overlap between timers and reduce the wakeup from idle. > > Optimising the ilb selection should significantly improve > experimental results for this patch. > > 2) The timer test driver creates quite large timer load so that the > effect of migration is observable as sleep time difference on the > expected target cpu. This kind of timer load may not be uncommon > with lots of application stack loaded in an enterprise system the important thing to watch out for is to not have _worse_ performance due to ilb jumping too much. So as long as you can prove that numbers dont get worse you are golden. Power-saving via migration will only work if there's a concentrated workload to begin with. So the best results will be in combination with scheduler power-saving patches. (which too make the ilb jump less in essence) So by getting scheduler power saving enhancements your method will work better too - there's good synergy and no dependency on any user-space component. Btw., could you please turn the runtime switch into a /proc/sys sysctl, and only when CONFIG_SCHED_DEBUG=y. Otherwise it should be default-enabled with no ability to turn it off. Ingo _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
