netdev - Re: [PATCH net] net: sched: shrink struct qdisc_skb

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Message-ID: <CAJ3xEMhMO7wydorRivtvSgJr9LBjRpYDJtbYfgd0ACPLYBXyzw@mail.gmail.com>
Date:	Fri, 19 Sep 2014 00:28:17 +0300
From:	Or Gerlitz <gerlitz.or@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Stephen Hemminger <stephen@...workplumber.org>,
	Govindarajulu Varadarajan <_govind@....com>,
	Yinghai Lu <yinghai@...nel.org>,
	David Miller <davem@...emloft.net>,
	NetDev <netdev@...r.kernel.org>, ssujith@...co.com,
	gvaradar@...co.com, "Christian Benvenuti (benve)" <benve@...co.com>
Subject: Re: [PATCH net] net: sched: shrink struct qdisc_skb_cb to 28 bytes

On Thu, Sep 18, 2014 at 7:32 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2014-09-18 at 09:26 -0700, Stephen Hemminger wrote:
>> On Thu, 18 Sep 2014 08:02:05 -0700
>> Eric Dumazet <eric.dumazet@...il.com> wrote:
>>
>> > From: Eric Dumazet <edumazet@...gle.com>
>> >
>> > We cannot make struct qdisc_skb_cb bigger without impacting IPoIB,
>> > or increasing skb->cb[] size.
>> >
>> > Commit e0f31d849867 ("flow_keys: Record IP layer protocol in
>> > skb_flow_dissect()") broke IPoIB.
>> >
>> > Only current offender is sch_choke, and this one do not need an
>> > absolutely precise flow key.
>> >
>> > If we store 17 bytes of flow key, its more than enough. (Its the actual
>> > size of flow_keys if it was a packed structure, but we might add new
>> > fields at the end of it later)
>> >
>> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>>
>> Can we add BUILD_BUG to stop next time something smacks this.
>
> I though we had.
>
> Maybe IPoIB lacks one.
>
> Or, do you have an idea ?

Nope, we currently don't have such build time check, I saw you posted
one and I will be able to test it Sunday.
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