netdev - Re: [PATCH net-next] net: sched: shrink struct Qdisc

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Date:   Fri, 25 May 2018 16:41:28 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH net-next] net: sched: shrink struct Qdisc

Fri, May 25, 2018 at 04:28:44PM CEST, pabeni@...hat.com wrote:
>The struct Qdisc has a lot of holes, especially after commit
>a53851e2c321 ("net: sched: explicit locking in gso_cpu fallback"),
>which as a side effect, moved the fields just after 'busylock'
>on a new cacheline.
>
>Since both 'padded' and 'refcnt' are not updated frequently, and
>there is a hole before 'gso_skb', we can move such fields there,
>saving a cacheline without any performance side effect.
>
>Before this commit:
>
>pahole -C Qdisc net/sche/sch_generic.o
>	# ...
>        /* size: 384, cachelines: 6, members: 25 */
>        /* sum members: 236, holes: 3, sum holes: 92 */
>        /* padding: 56 */
>
>After this commit:
>pahole -C Qdisc net/sche/sch_generic.o
>	# ...
>	/* size: 320, cachelines: 5, members: 25 */
>	/* sum members: 236, holes: 2, sum holes: 28 */
>	/* padding: 56 */
>
>Signed-off-by: Paolo Abeni <pabeni@...hat.com>

Acked-by: Jiri Pirko <jiri@...lanox.com>