On 03/27/2013 06:30 PM, Vincent Guittot wrote: >> Arguing the performance/power balance does no much sense without >> > detailed scenario. We just want to seek a flexible compromise way. >> > But fixed buddy cpu is not flexible. and it may lose many possible >> > powersaving fit scenarios on x86 system. Like if 2 SMT cpu can handle >> > all tasks, we don't need to wake another core. or if 2 cores in one >> > socket can handle tasks, we also don't need to wakeup another socket. > Using 2 SMT for all tasks implies to accept latency and to share > resources like cache and memory bandwidth so it means that you also > accept some potential performance decrease which implies that someone > must select this mode with a knob. > The primary goal of the patchset is not to select between powersaving > and performance but to stay in performance mode. We pack the small > tasks in one CPU so the performance will not decrease but the low load > scenario will consume less power. Then, I can add another step which > will be more power saving aggressive with a potential cost of > performance and i this case the buddy CPU will be updated dynamically > according to the system load >
Predication of small task behavior is often wrong. so for performance purpose, packing task is a bad idea. -- Thanks Alex -- 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/