On 8/10/2022 10:51 PM, Paul E. McKenney wrote: > On Wed, Aug 10, 2022 at 10:31:56PM -0400, Joel Fernandes wrote: >> >> >> On 8/10/2022 10:23 PM, Joel Fernandes wrote: >>> >>> >>> On 8/8/2022 11:45 PM, Joel Fernandes (Google) wrote: >>>> Just a refresh of v3 with one additional debug patch. v3's cover letter is here: >>>> https://lore.kernel.org/all/20220713213237.1596225-1-joel@xxxxxxxxxxxxxxxxx/ >>>> >>>> I just started working on this again while I have some time during paternity >>>> leave ;-) So I thought I'll just send it out again. No other changes other >>>> than that 1 debug patch I added on the top. >>>> >>>> Next I am going to go refine the power results as mentioned in Paul's comments >>>> on the last cover letter. >>> >>> Side note: Here is another big selling point for call_rcu_lazy(). >>> Instead of _lazy(), if you just increased jiffies_till_first_fqs, and >>> slowed *all* call_rcu() down to achieve the same effect, that would >>> affect percpu refcounters switching to atomic-mode, for example. >>> >>> They switch to atomic mode by calling __percpu_ref_switch_mode() which >>> is called by percpu_ref_switch_to_atomic_sync().> >>> This will slow this call down for the full lazy duration which will slow >>> down suspend in blk_pre_runtime_suspend(). >> >> Correction while I am going on the record (got to be careful these >> days). It *might* slow down RCU for the full lazy duration, unless of >> course a fly-by rescue call_rcu() comes in. > > Just unload a module, which if I remember correctly invokes rcu_barrier(). > Lots of rescue callbacks. ;-) Haha. Yes I suppose the per-cpu atomic switch paths can also invoke rcu_barrier() but I suspect somebody might complain about IPIs :-P Thanks, - Joel
