On Mon, Mar 11, 2019 at 08:19:47AM -0700, Paul E. McKenney wrote: > This time keeping the CC list... > > Thanx, Paul > > On Mon, Mar 11, 2019 at 08:18:54AM -0700, Paul E. McKenney wrote: > > On Mon, Mar 11, 2019 at 03:16:11PM +0530, Neeraj Upadhyay wrote: > > > Current code does not call adjust_jiffies_till_sched_qs(), > > > if jiffies_till_sched_qs is specified. For the case, where > > > jiffies_till_first_fqs and jiffies_till_next_fqs are default, > > > jiffies_to_sched_qs won't be a correct adjustment of > > > jiffies_till_sched_qs. > > > > > > Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx> > > > > Good catch! Queued and pushed. Please see below for updated > > commit log. On future patches, could you please first describe > > the problem and consequences, then what the fix is? This approach > > makes it much easier for people later on who will be trying to > > figure out what is going on, and who might or might not have much > > understanding of RCU. (For example, they might be doing a bisection > > or some such.) > > > > Not a big deal, as I can touch this up, but a good habit to get into. > > > > And no, rcutorture currently does not specify non-default values > > for jiffies_till_sched_qs. Which should probably be fixed. I could > > make rcu_implicit_dynticks_qs() complain if jiffies_to_sched_qs is > > zero, but that feels a bit hacky and specific. :-/ > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit ee474b85fa0815be940ed89a91e0d84a110a0a92 > > Author: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx> > > Date: Mon Mar 11 15:16:11 2019 +0530 > > > > rcu: Default jiffies_to_sched_qs to jiffies_till_sched_qs > > > > The current code only calls adjust_jiffies_till_sched_qs() if > > jiffies_till_sched_qs is left at its default value, so when the > > jiffies_till_sched_qs kernel-boot parameter actually is specified, > > jiffies_to_sched_qs will be left with the value zero, which > > will result in useless slowdowns of cond_resched(). This commit > > therefore changes rcu_init_geometry() to unconditionally invoke > > adjust_jiffies_till_sched_qs(), which ensures that jiffies_to_sched_qs > > will be initialized in all cases, thus maintaining good cond_resched() > > performance. > > > > Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx> > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx> > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index ddd5c74e386b..10aeb89395ea 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -3259,8 +3259,7 @@ static void __init rcu_init_geometry(void) > > jiffies_till_first_fqs = d; > > if (jiffies_till_next_fqs == ULONG_MAX) > > jiffies_till_next_fqs = d; > > - if (jiffies_till_sched_qs == ULONG_MAX) > > - adjust_jiffies_till_sched_qs(); > > + adjust_jiffies_till_sched_qs(); > > > > /* If the compile-time values are accurate, just leave. */ > > if (rcu_fanout_leaf == RCU_FANOUT_LEAF && > Makes sense to me. Also the comment here needs an update too I think: static ulong jiffies_to_sched_qs; /* Adjusted version of above if not default */ Seems to me, after your patch jiffies_to_sched_qs will always be an adjusted value of some sort, unless jiffies_till_sched_qs is specified. Comment should be some thing like this then? /* Either the above, or an adjusted default version based on * jiffies_till_{first,next}_fqs if it is not specified */ thanks, - Joel