Re: [PATCH net] net: sched: shrink struct qdisc_skb_cb to 28 bytes

On Thu, Sep 18, 2014 at 7:32 PM, Eric Dumazet [off-list ref] wrote:

On Thu, 2014-09-18 at 09:26 -0700, Stephen Hemminger wrote:

quoted

On Thu, 18 Sep 2014 08:02:05 -0700
Eric Dumazet [off-list ref] wrote:

quoted

From: Eric Dumazet <edumazet@google.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@google.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.