netdev - Re: [PATCH -next 3/4] sched: remove qdisc_rehape

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Message-ID: <1465423725.7945.25.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Wed, 08 Jun 2016 15:08:45 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Florian Westphal <fw@...len.de>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH -next 3/4] sched: remove qdisc_rehape_fail

On Wed, 2016-06-08 at 23:01 +0200, Florian Westphal wrote:

> 
> Would you mind an annotation rather than covering the hole?
> 
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -71,11 +71,11 @@ struct Qdisc {
>         struct gnet_stats_basic_cpu __percpu *cpu_bstats;
>         struct gnet_stats_queue __percpu *cpu_qstats;
>  
> -       struct Qdisc            *next_sched;
> -       struct sk_buff          *gso_skb;
>         /*
>          * For performance sake on SMP, we put highly modified fields at the end
>          */
> +       struct Qdisc            *next_sched ____cacheline_aligned_in_smp;
> +       struct sk_buff          *gso_skb;
> 
> 
> ... it creates 16 byte hole after cpu_qstats and keeps the rest as-is
>  (i.e. next_sched is at beginning of 2nd cacheline, as before the removal).
> 
> I could also cover the hole by moving rcu_head there but it seems fragile
> and doesn't reduce total struct size anyway (we get larger hole at end).
> 
> If you have no objection I'd resubmit the series as-is but with this patch.
> 
> Let me know, thanks Eric!

This all looks fine to me.