On 2021-01-21 13:38:34 [+0100], Uladzislau Rezki wrote: > __get_free_page() returns "unsigned long" whereas a bnode is a pointer > to kvfree_rcu_bulk_data struct, without a casting the compiler will > emit a warning. Yes, learned about it, sorry. > >> You think that a CPU migration is a bad thing. But why? > >> > It is not a bad thing. But if it happens we might queue a new bnode > to a drain list of another CPU where a previous element of a new > bnode may be just underutilized. So that is why i use migrate_disable()/enable() > to prevent it. If you allocate a node for queueing and then you realize that you already have one then you either free it or queue it for later. Given that all this is a slower-path and that this is used on every-CPU, sooner or later that page will be used avoids a later allocation, right? > If there are some hidden issues with migrate_disable()/enable() or you > think it is a bad idea to use it, it would be appreciated if you could > describe your view in more detail. Just what I mentioned in my previous email: - the whole operation isn't cheap but it is more efficient in tree compared to what we used to have in RT. - the task can no be freely placed while it could run. So if the task gets preempted, it will have to wait until it can run on the CPU again. Sebastian
