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 &&
