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Date:   Wed, 17 Jan 2018 07:33:38 +0000
From:   Nogah Frankel <nogahf@...lanox.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "jiri@...nulli.us" <jiri@...nulli.us>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "oss-drivers@...ronome.com" <oss-drivers@...ronome.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        Yuval Mintz <yuvalm@...lanox.com>
Subject: RE: [PATCH net-next v2] net: sched: red: don't reset the backlog on
 every stat dump

> -----Original Message-----
> From: Jakub Kicinski [mailto:jakub.kicinski@...ronome.com]
> Sent: Monday, January 15, 2018 6:01 AM
> To: davem@...emloft.net; jiri@...nulli.us; Nogah Frankel
> <nogahf@...lanox.com>
> Cc: netdev@...r.kernel.org; oss-drivers@...ronome.com;
> xiyou.wangcong@...il.com; edumazet@...gle.com; Yuval Mintz
> <yuvalm@...lanox.com>; Jakub Kicinski <jakub.kicinski@...ronome.com>
> Subject: [PATCH net-next v2] net: sched: red: don't reset the backlog on every
> stat dump
> 
> 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@...ronome.com>

Acked-by: Nogah Frankel <nogahf@...lanox.com>

Thanks
Nogah

> ---
> v2:
>  - reuse the mlxsw infra added for prio;
>  - align the way qstats are passed with prio.
> 
>  .../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(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
> b/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
> index e11a0abfc663..8cac5202b913 100644
> --- 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(struct
> mlxsw_sp_port *mlxsw_sp_port,
> 
>  	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_sp_port
> *mlxsw_sp_port,
>  						 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 mlxsw_sp_port
> *mlxsw_sp_port,
>  			     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
> mlxsw_sp_port *mlxsw_sp_port,
>  		     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_sp_qdisc_ops_red = {
>  	.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,
> diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
> index 9c341f003091..cc23c041a6d7 100644
> --- 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 {
> diff --git a/net/sched/sch_red.c b/net/sched/sch_red.c
> index 0af1c1254e0b..16644b3d2362 100644
> --- a/net/sched/sch_red.c
> +++ b/net/sched/sch_red.c
> @@ -167,6 +167,7 @@ static int red_offload(struct Qdisc *sch, bool enable)
>  		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;
>  	}
> @@ -322,7 +323,6 @@ static int red_dump(struct Qdisc *sch, struct sk_buff
> *skb)
>  	};
>  	int err;
> 
> -	sch->qstats.backlog = q->qdisc->qstats.backlog;
>  	err = red_dump_offload_stats(sch, &opt);
>  	if (err)
>  		goto nla_put_failure;
> --
> 2.15.1

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