On Tue, Jan 17, 2017 at 06:53:46PM -0800, Paul E. McKenney wrote:
> Commit d2db185bfee8 ("rcu: Remove short-term CPU kicking") removed
> frequent calls to resched_cpu(), which means that the only time
> resched_cpu() is invoked is after an RCU CPU stall warning. Although
> this is good from an avoid-IPIs perspective, we should try to break
> things loose -before- splatting. This commit therefore starts invoking
> resched_cpu() for each holdout at each force-quiescent-state interval
> that is more than halfway through the stall-warning interval.
Just realized an issue with this commit message: you're referring to
what now appears as patch 8 in the past tense as something already done,
and with a commit ID that probably doesn't work anymore. You need to
rephrase this to describe how it leads to a *subsequent* change rather
than fixing something already changed.
With the commit message fixed:
Reviewed-by: Josh Triplett <j...@joshtriplett.org>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> ---
> kernel/rcu/tree.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 83bf054e194e..0e61b62e3f4a 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data
> *rdp,
> 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. */
> + /*
> + * If more than halfway to RCU CPU stall-warning time, do
> + * a resched_cpu() to try to loosen things up a bit.
> + */
> + if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
> + resched_cpu(rdp->cpu);
>
> return 0;
> }
> --
> 2.5.2
>
