netdev - Re: [PATCH net-next v6 3/3] act_vlan: VLAN action rewrite to use RCU lock/unlock and update

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Date:   Tue, 7 Nov 2017 17:08:16 +0000
From:   Pieter Jansen van Vuuren <pieter.jansenvanvuuren@...ronome.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Manish Kurup <kurup.manish@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Simon Horman <simon.horman@...ronome.com>,
        john.hurley@...ronome.com, oss-drivers@...ronome.com,
        Netdev <netdev@...r.kernel.org>, aring@...atatu.com,
        Roman Mashak <mrv@...atatu.com>,
        Manish Kurup <manish.kurup@...izon.com>
Subject: Re: [PATCH net-next v6 3/3] act_vlan: VLAN action rewrite to use
 RCU lock/unlock and update

On Tue, 7 Nov 2017 08:54:20 -0800
Alexander Duyck <alexander.duyck@...il.com> wrote:

> On Mon, Nov 6, 2017 at 10:37 AM, Pieter Jansen van Vuuren
> <pieter.jansenvanvuuren@...ronome.com> wrote:
> > On Fri,  3 Nov 2017 11:50:47 -0400
> > Manish Kurup <kurup.manish@...il.com> wrote:
> >  
> >> Using a spinlock in the VLAN action causes performance issues when
> >> the VLAN action is used on multiple cores. Rewrote the VLAN action to
> >> use RCU read locking for reads and updates instead.
> >>
> >> Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
> >> Acked-by: Jiri Pirko <jiri@...lanox.com>
> >> Signed-off-by: Manish Kurup <manish.kurup@...izon.com>
> >> ---
> >>  include/net/tc_act/tc_vlan.h | 46 +++++++++++++++++++++------
> >>  net/sched/act_vlan.c         | 75
> >> ++++++++++++++++++++++++++++++-------------- 2 files changed, 88
> >> insertions(+), 33 deletions(-)  
> > ...  
> >>
> >> +static void tcf_vlan_cleanup(struct tc_action *a, int bind)
> >> +{
> >> +     struct tcf_vlan *v = to_vlan(a);
> >> +     struct tcf_vlan_params *p;
> >> +
> >> +     p = rcu_dereference_protected(v->vlan_p, 1);
> >> +     kfree_rcu(p, rcu);
> >> +}
> >> +
> >>  static int tcf_vlan_dump(struct sk_buff *skb, struct tc_action *a,
> >>                        int bind, int ref)
> >>  {
> >>       unsigned char *b = skb_tail_pointer(skb);
> >>       struct tcf_vlan *v = to_vlan(a);
> >> +     struct tcf_vlan_params *p = rtnl_dereference(v->vlan_p);  
> > nack. This fails reverse xmas-tree.  
> 
> Are we really going to be so strict about the reverse xmas-tree that
> we won't allow for assignment w/ variable declaration because the
> dependency order won't fit into that format?
Okay, I think that is a fair point. I would be okay by making an exception
for this.
> 
> Last I knew this kind of setup was an exception to the reverse
> xmas-tree layout requirement because in this case 'p' relies on 'v' so
> we can't reorder these without having to kick the assignment of 'p'
> off onto a line by itself.
I was actually not aware of this, thank you for pointing it out. It does
make sense.
> 
> - Alex