On 8/30/2022 12:44 PM, Uladzislau Rezki wrote: > Hello, Frederic. > >> >> Although who knows, may be some periodic file operation while idle are specific >> to Android. I'll try to trace lazy callbacks while idle and the number of grace >> periods associated. >> >> > Everything related to lazy call-backs is about not waking "nocb" > kthreads in order to offload one or i should say few callbacks > because it is more or less useless. Currently if incoming callback > is the only one, it will kick a GP whereas a GP will kick nocb_kthread > to offload. > > In "light" loaded test cases, especially where a power drain is a key > thing, such light load may lead to some kind of "noise" produced by the > RCU core, i.e. kicking idle CPUs, thus wasting power. On our ARM devices > it is not painful, but there is a small power gain and it is visible. > For other systems, like Joel measures for Intel SoC it is more visible, > because of a power cost getting in/out of isle states. Indeed! And Intel (Rushikesh) reminded me today that it has become more important than before to not disturb idle CPUs, because more and more pieces of hardware are moving into SoCs. So if the whole SoC cannot go into deeper sleep state (package C-state) because of the CPU getting disturbed, then that's lesser power savings than say in the not-so-recent past. Rushikesh could shed more light on that fact. Thanks, - Joel
