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

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Date:   Mon, 28 May 2018 23:13:50 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     pabeni@...hat.com
Cc:     netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us
Subject: Re: [PATCH net-next] net: sched: shrink struct Qdisc

From: Paolo Abeni <pabeni@...hat.com>
Date: Fri, 25 May 2018 16:28:44 +0200

> 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>

Applied.