On Wed, Sep 23, 2020 at 11:22:08AM -0400, Joel Fernandes (Google) wrote: > Currently, rcu_do_batch() depends on the unsegmented callback list's len field > to know how many CBs are executed. This fields counts down from 0 as CBs are > dequeued. It is possible that all CBs could not be run because of reaching > limits in which case the remaining unexecuted callbacks are requeued in the > CPU's segcblist. > > The number of callbacks that were not requeued are then the negative count > (how > many CBs were run) stored in the rcl->len which has been counting down on > every > dequeue. This negative count is then added to the per-cpu segmented callback > list's to correct its count. > > Such a design works against future efforts to track the length of each segment > of the segmented callback list. The reason is because > rcu_segcblist_extract_done_cbs() will be populating the unsegmented callback > list's length field (rcl->len) during extraction. > Also, the design of counting down from 0 is confusing and error-prone IMHO.
Right :) > > This commit therefore explicitly counts have many callbacks were executed in s/have/how > rcu_do_batch() itself, and uses that to update the per-CPU segcb list's ->len > field, without relying on the negativity of rcl->len. > > Signed-off-by: Joel Fernandes (Google) <[email protected]> Reviewed-by: Frederic Weisbecker <[email protected]> Thanks.
