On Mon, May 14, 2018 at 12:20:28PM -0700, Paul E. McKenney wrote:
> On Sun, May 13, 2018 at 08:15:40PM -0700, Joel Fernandes (Google) wrote:
> > Currently the tree RCU clean up code records a CleanupMore trace event
> > even if the GP was already in progress. This makes CleanupMore show up
> > twice for no reason. Avoid it.
> >
> > Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org>
>
> Good catch, and I applied this patch. I did rework the commit log
> a bit, so please look it over to make sure I didn't mess it up.
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit 52c4e689efd975f5383895b1bc1b91bc90fdd372
> Author: Joel Fernandes (Google) <j...@joelfernandes.org>
> Date: Sun May 13 20:15:40 2018 -0700
>
> rcu: Produce last "CleanupMore" trace only if late-breaking request
>
> Currently the tree RCU clean-up code records a "CleanupMore" trace
> event in response to late-arriving grace-period requests even if the
> grace period was already requested. This makes "CleanupMore" show up an
> extra time (in addition to once for each rcu_node structure that was
> previously marked with the request) for no good reason. This commit
> therefore avoids emitting this trace message unless the only if the only
> request for this next grace period arrived during or after the cleanup
> scan of the rcu_node structures.
Yes, this is fine except "unless the only if the only" should be "unless the".
thanks,
- Joel
>
> Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 8063a0478870..de6447dd73de 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2072,7 +2072,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
> rsp->gp_state = RCU_GP_IDLE;
> /* Check for GP requests since above loop. */
> rdp = this_cpu_ptr(rsp->rda);
> - if (ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
> + if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
> trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
> TPS("CleanupMore"));
> needgp = true;
>
