On Thu, Oct 06, 2022 at 11:55:43AM -0700, Paul E. McKenney wrote: > On Tue, Oct 04, 2022 at 02:41:46AM +0000, Joel Fernandes (Google) wrote: > > v7 version of RCU lazy patches based on rcu/next branch. > > > > To facilitate easier merge, I dropped tracing and other patches and just > > implemented the new changes. I will post the tracing patches later along with > > rcutop as I need to add new tracepoints that Frederic suggested. > > > > Main recent changes: > > 1. rcu_barrier() wake up only for lazy bypass list. > > 2. Make all call_rcu() default-lazy and add call_rcu_flush() API. > > 3. Take care of some callers using call_rcu_flush() API. > > 4. Several refactorings suggested by Paul/Frederic. > > 5. New call_rcu() to call_rcu_flush() conversions by Joel/Vlad/Paul. > > > > I am seeing good performance and power with these patches on real ChromeOS x86 > > asymmetric hardware. > > > > Earlier cover letter with lots of details is here: > > https://lore.kernel.org/all/20220901221720.1105021-1-joel@xxxxxxxxxxxxxxxxx/ > > > > List of recent changes: > > > > [ Frederic Weisbec: Program the lazy timer only if WAKE_NOT, since other > > deferral levels wake much earlier so for those it is not needed. ] > > > > [ Frederic Weisbec: Use flush flags to keep bypass API code clean. ] > > > > [ Frederic Weisbec: Make rcu_barrier() wake up only if main list empty. ] > > > > [ Frederic Weisbec: Remove extra 'else if' branch in rcu_nocb_try_bypass(). ] > > > > [ Joel: Fix issue where I was not resetting lazy_len after moving it to rdp ] > > > > [ Paul/Thomas/Joel: Make call_rcu() default lazy so users don't mess up. ] > > > > [ Paul/Frederic : Cosmetic changes, split out wakeup of nocb thread. ] > > > > [ Vlad/Joel : More call_rcu -> flush conversions ] > > Thank you for your continued work on this! > > I pulled these into an experimental branch, applied Uladzislau's > Tested-by and ran a quick round of rcutorture. > > From TREE02, TREE03, and TREE09 I got this: > > In file included from kernel/rcu/tree.c:68: > kernel/rcu/tree.h:449:13: error: ‘wake_nocb_gp’ used but never defined [-Werror] > 449 | static bool wake_nocb_gp(struct rcu_data *rdp, bool force); > | ^~~~~~~~~~~~ > > One could argue that this is not a big deal, except that Linus gets a > bit tetchy when this sort of thing shows up in mainline. > Sorry. I have not tested TREE02, TREE03 and TREE09 scenarios. My goal was to check below functionalities: - call_rcu_flush() does not introduce any delays once it is queued - call_rcu() does not apply pressure on the RCU-machinery from wake-up point of view - boot-time is not degraded - synchronize_rcu() and rcu_barrier() work as expected - if bypass consists of lazy callbacks the *flush() one has to initiate the offloading -- Uladzislau Rezki
