netdev - Re: [PATCH net-next] net/sched: get rid of qdisc->padded

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Date:   Fri, 9 Oct 2020 09:35:03 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Allen Pais <allen.lkml@...il.com>
Subject: Re: [PATCH net-next] net/sched: get rid of qdisc->padded

On Fri, Oct 9, 2020 at 2:18 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed,  7 Oct 2020 09:51:11 -0700 Eric Dumazet wrote:
> > diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
> > index 6c762457122fd0091cb0f2bf41bda73babc4ac12..d8fd8676fc724110630904909f64d7789f3a4b47 100644
> > --- a/include/net/sch_generic.h
> > +++ b/include/net/sch_generic.h
> > @@ -91,7 +91,7 @@ struct Qdisc {
> >       struct net_rate_estimator __rcu *rate_est;
> >       struct gnet_stats_basic_cpu __percpu *cpu_bstats;
> >       struct gnet_stats_queue __percpu *cpu_qstats;
> > -     int                     padded;
> > +     int                     pad;
> >       refcount_t              refcnt;
> >
> >       /*
>
> Hi Eric!
>
> Why keep the pad field? the member to lines down is
> __cacheline_aligned, so we shouldn't have to manually
> push things out?
>
>         struct gnet_stats_queue __percpu *cpu_qstats;
>         int                     pad;

I usually prefer adding explicit fields to tell where the holes are,
for future reuse.
Not many developers are aware of pahole existence :/
I renamed it to pad, I could have used padding or something else.