Re: [net-next PATCH 05/15] net: sched: a dflt qdisc may be used with per cpu stats

On 16-08-24 09:41 AM, Eric Dumazet wrote:

On Tue, 2016-08-23 at 13:24 -0700, John Fastabend wrote:

quoted

Enable dflt qdisc support for per cpu stats before this patch a
dflt qdisc was required to use the global statistics qstats and
bstats.

Signed-off-by: John Fastabend <redacted>
---
 net/sched/sch_generic.c |   24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 80544c2..910b4d15 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c

@@ -646,18 +646,34 @@ struct Qdisc *qdisc_create_dflt(struct netdev_queue *dev_queue,
 	struct Qdisc *sch;
 
 	if (!try_module_get(ops->owner))
-		goto errout;
+		return NULL;
 
 	sch = qdisc_alloc(dev_queue, ops);
 	if (IS_ERR(sch))
-		goto errout;
+		return NULL;
 	sch->parent = parentid;
 
-	if (!ops->init || ops->init(sch, NULL) == 0)
+	if (!ops->init)
 		return sch;
 
-	qdisc_destroy(sch);
+	if (ops->init(sch, NULL))
+		goto errout;
+
+	/* init() may have set percpu flags so init data structures */
+	if (qdisc_is_percpu_stats(sch)) {
+		sch->cpu_bstats =
+			netdev_alloc_pcpu_stats(struct gnet_stats_basic_cpu);
+		if (!sch->cpu_bstats)
+			goto errout;
+
+		sch->cpu_qstats = alloc_percpu(struct gnet_stats_queue);
+		if (!sch->cpu_qstats)
+			goto errout;
+	}
+

Why are you attempting these allocations here instead of qdisc_alloc()

This looks weird, I would expect base qdisc being fully allocated before
ops->init() is attempted.

I could fully allocate it in qdisc_alloc() but we don't know if the
qdisc needs per cpu data structures until after the init call. So it
would sit unused in those cases if done from qdisc_alloc(). It seems
best to me at least to just avoid the allocation in qdisc_alloc() and
do it after init like I did here.

Perhaps it would be nice to pull these into a function call
post_init_qdisc_alloc() that does all this allocation?

.John