netdev - Re: [PATCH net-next v2] net: sched: red: don't reset the backlog on every stat dump

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Message-Id: <20180116.140502.1023255989015569679.davem@davemloft.net>
Date:   Tue, 16 Jan 2018 14:05:02 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     jakub.kicinski@...ronome.com
Cc:     jiri@...nulli.us, nogahf@...lanox.com, netdev@...r.kernel.org,
        oss-drivers@...ronome.com, xiyou.wangcong@...il.com,
        edumazet@...gle.com, yuvalm@...lanox.com
Subject: Re: [PATCH net-next v2] net: sched: red: don't reset the backlog
 on every stat dump

From: Jakub Kicinski <jakub.kicinski@...ronome.com>
Date: Sun, 14 Jan 2018 20:01:26 -0800

> 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>

Jiri, please review.

Thanks.