From: Jakub Kicinski <jakub.kicinski@netronome.com>
Date: Sun, 14 Jan 2018 20:01:26 -0800
Subject: net: sched: red: don't reset the backlog on every stat dump
Patch-mainline: v4.16-rc1
Git-commit: 416ef9b15c688b91edbf654ebe7bc349c9151147
References: bsc#1109837

Commit 0dfb33a0d7e2 ("sch_red: report backlog information") copied
child's backlog into RED's backlog.  Back then RED did not maintain
its own backlog counts.  This has changed after commit 2ccccf5fb43f
("net_sched: update hierarchical backlog too") and commit d7f4f332f082
("sch_red: update backlog as well").  Copying is no longer necessary.

Tested:

$ tc -s qdisc show dev veth0
qdisc red 1: root refcnt 2 limit 400000b min 30000b max 30000b ecn
 Sent 20942 bytes 221 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 1260b 14p requeues 14
  marked 0 early 0 pdrop 0 other 0
qdisc tbf 2: parent 1: rate 1Kbit burst 15000b lat 3585.0s
 Sent 20942 bytes 221 pkt (dropped 0, overlimits 138 requeues 0)
 backlog 1260b 14p requeues 14

Recently RED offload was added.  We need to make sure drivers don't
depend on resetting the stats.  This means backlog should be treated
like any other statistic:

  total_stat = new_hw_stat - prev_hw_stat;

Adjust mlxsw.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Nogah Frankel <nogahf@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c |   26 ++++++++++++++++---
 include/net/pkt_cls.h                                |    1 
 net/sched/sch_red.c                                  |    2 -
 3 files changed, 25 insertions(+), 4 deletions(-)

--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
@@ -247,6 +247,8 @@ mlxsw_sp_setup_tc_qdisc_red_clean_stats(
 
 	stats_base->overlimits = red_base->prob_drop + red_base->prob_mark;
 	stats_base->drops = red_base->prob_drop + red_base->pdrop;
+
+	stats_base->backlog = 0;
 }
 
 static int
@@ -306,6 +308,19 @@ mlxsw_sp_qdisc_red_replace(struct mlxsw_
 						 max, prob, p->is_ecn);
 }
 
+static void
+mlxsw_sp_qdisc_red_unoffload(struct mlxsw_sp_port *mlxsw_sp_port,
+			     struct mlxsw_sp_qdisc *mlxsw_sp_qdisc,
+			     void *params)
+{
+	struct tc_red_qopt_offload_params *p = params;
+	u64 backlog;
+
+	backlog = mlxsw_sp_cells_bytes(mlxsw_sp_port->mlxsw_sp,
+				       mlxsw_sp_qdisc->stats_base.backlog);
+	p->qstats->backlog -= backlog;
+}
+
 static int
 mlxsw_sp_qdisc_get_red_xstats(struct mlxsw_sp_port *mlxsw_sp_port,
 			      struct mlxsw_sp_qdisc *mlxsw_sp_qdisc,
@@ -338,7 +353,7 @@ mlxsw_sp_qdisc_get_red_stats(struct mlxs
 			     struct mlxsw_sp_qdisc *mlxsw_sp_qdisc,
 			     struct tc_qopt_offload_stats *stats_ptr)
 {
-	u64 tx_bytes, tx_packets, overlimits, drops;
+	u64 tx_bytes, tx_packets, overlimits, drops, backlog;
 	u8 tclass_num = mlxsw_sp_qdisc->tclass_num;
 	struct mlxsw_sp_qdisc_stats *stats_base;
 	struct mlxsw_sp_port_xstats *xstats;
@@ -354,14 +369,18 @@ mlxsw_sp_qdisc_get_red_stats(struct mlxs
 		     stats_base->overlimits;
 	drops = xstats->wred_drop[tclass_num] + xstats->tail_drop[tclass_num] -
 		stats_base->drops;
+	backlog = xstats->backlog[tclass_num];
 
 	_bstats_update(stats_ptr->bstats, tx_bytes, tx_packets);
 	stats_ptr->qstats->overlimits += overlimits;
 	stats_ptr->qstats->drops += drops;
 	stats_ptr->qstats->backlog +=
-			mlxsw_sp_cells_bytes(mlxsw_sp_port->mlxsw_sp,
-					     xstats->backlog[tclass_num]);
+				mlxsw_sp_cells_bytes(mlxsw_sp_port->mlxsw_sp,
+						     backlog) -
+				mlxsw_sp_cells_bytes(mlxsw_sp_port->mlxsw_sp,
+						     stats_base->backlog);
 
+	stats_base->backlog = backlog;
 	stats_base->drops +=  drops;
 	stats_base->overlimits += overlimits;
 	stats_base->tx_bytes += tx_bytes;
@@ -375,6 +394,7 @@ static struct mlxsw_sp_qdisc_ops mlxsw_s
 	.type = MLXSW_SP_QDISC_RED,
 	.check_params = mlxsw_sp_qdisc_red_check_params,
 	.replace = mlxsw_sp_qdisc_red_replace,
+	.unoffload = mlxsw_sp_qdisc_red_unoffload,
 	.destroy = mlxsw_sp_qdisc_red_destroy,
 	.get_stats = mlxsw_sp_qdisc_get_red_stats,
 	.get_xstats = mlxsw_sp_qdisc_get_red_xstats,
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -748,6 +748,7 @@ struct tc_red_qopt_offload_params {
 	u32 max;
 	u32 probability;
 	bool is_ecn;
+	struct gnet_stats_queue *qstats;
 };
 
 struct tc_red_qopt_offload {
--- a/net/sched/sch_red.c
+++ b/net/sched/sch_red.c
@@ -166,6 +166,7 @@ static int red_offload(struct Qdisc *sch
 		opt.set.max = q->parms.qth_max >> q->parms.Wlog;
 		opt.set.probability = q->parms.max_P;
 		opt.set.is_ecn = red_use_ecn(q);
+		opt.set.qstats = &sch->qstats;
 	} else {
 		opt.command = TC_RED_DESTROY;
 	}
@@ -320,7 +321,6 @@ static int red_dump(struct Qdisc *sch, s
 	};
 	int err;
 
-	sch->qstats.backlog = q->qdisc->qstats.backlog;
 	err = red_dump_offload_stats(sch, &opt);
 	if (err)
 		goto nla_put_failure;