Messages in this thread | | | Date | Mon, 28 Nov 2016 02:58:09 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 2/2] rcu: Force resched_cpu when jiffies >= rcu_state.jiffies_resched |
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On Mon, Nov 28, 2016 at 03:46:39PM +0900, Byungchul Park wrote: > On Sat, Nov 26, 2016 at 04:00:46AM -0800, Paul E. McKenney wrote: > > On Fri, Nov 25, 2016 at 12:34:26AM -0800, Paul E. McKenney wrote: > > > On Tue, Nov 22, 2016 at 05:12:20PM +0900, Byungchul Park wrote: > > > > On Wed, Nov 09, 2016 at 03:32:15PM +0900, Byungchul Park wrote: > > > > > Currently rcu code forces CPU into scheduler when jiffies >= > > > > > rcu_state.gp_start + jiffies_till_sched_qs, via resched_cpu(). > > > > > > > > > > It would be better to force CPU into scheduler when jiffies >= > > > > > rcu_state.jiffies_resched, too. > > > > > > > > Hello, > > > > > > > > I think these two patches are necessary to call resched_cpu() even in > > > > case of jiffies >= rcu_state.jiffies_resched, too. Am I wrong? > > > > > > > > It would be appriciated if you let me know if I was wrong. > > > > > > My current thought is that both the "if" statement and the call to > > > resched_cpu() should be removed, but I am still testing and working > > > through the timing. > > > > > > Either way, I do very much appreciate your having called my attention > > > to this code! > > > > And the patch shown below seems to do the trick. Thoughts? > > Hello, > > I see.. I didn't check the log 'rcu: Stop treating in-kernel CPU-bound > workloads as errors'. > > If you are convinced to remove them, no objection.
It is quite possible that additional time-related adjustments are needed, but this change is a step in the right direction.
Thanx, Paul
> Thank you, > Byungchul > > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit d2db185bfee894c573faebed93461e9938bdbb61 > > Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > Date: Fri Nov 25 00:07:23 2016 -0800 > > > > rcu: Remove short-term CPU kicking > > > > Commit 4914950aaa12d ("rcu: Stop treating in-kernel CPU-bound workloads > > as errors") added a (relatively) short-timeout call to resched_cpu(). > > This was inspired by as issue that was fixed by b7e7ade34e61 ("sched/core: > > Fix remote wakeups"). But given that this issue was fixed, it is time > > for the current commit to remove this call to resched_cpu(). > > > > Reported-by: Byungchul Park <byungchul.park@lge.com> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index 5f4f80d07852..91a68e4e6671 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -1345,12 +1345,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, > > rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */ > > } > > > > - /* And if it has been a really long time, kick the CPU as well. */ > > - if (ULONG_CMP_GE(jiffies, > > - rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) || > > - ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs)) > > - resched_cpu(rdp->cpu); /* Force CPU into scheduler. */ > > - > > return 0; > > } > > >
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