On 12/13/2012 10:17 AM, Alex Shi wrote: > On 12/12/2012 09:31 PM, Vincent Guittot wrote: >> During the creation of sched_domain, we define a pack buddy CPU for each CPU >> when one is available. We want to pack at all levels where a group of CPU can >> be power gated independently from others. >> On a system that can't power gate a group of CPUs independently, the flag is >> set at all sched_domain level and the buddy is set to -1. This is the default >> behavior. >> On a dual clusters / dual cores system which can power gate each core and >> cluster independently, the buddy configuration will be : >> >> | Cluster 0 | Cluster 1 | >> | CPU0 | CPU1 | CPU2 | CPU3 | >> ----------------------------------- >> buddy | CPU0 | CPU0 | CPU0 | CPU2 | >> >> Small tasks tend to slip out of the periodic load balance so the best place >> to choose to migrate them is during their wake up. The decision is in O(1) as >> we only check again one buddy CPU > > Just have a little worry about the scalability on a big machine, like on > a 4 sockets NUMA machine * 8 cores * HT machine, the buddy cpu in whole > system need care 64 LCPUs. and in your case cpu0 just care 4 LCPU. That > is different on task distribution decision.
In above big machine example, only one buddy cpu is not sufficient on each of level, like for 4 sockets level, maybe tasks can just full fill 2 sockets, then we just use 2 sockets, that is more performance/power efficient. But one buddy cpu here need to spread tasks to 4 sockets all. _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
