netdev - Re: [PATCH net-next v10 1/3] act_vlan: Change stats update to use per-core stats

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Date:   Thu, 9 Nov 2017 06:40:06 +0900
From:   Or Gerlitz <gerlitz.or@...il.com>
To:     Manish Kurup <kurup.manish@...il.com>
Cc:     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>,
        Pieter Jansen van Vuuren 
        <pieter.jansenvanvuuren@...ronome.com>,
        Simon Horman <simon.horman@...ronome.com>,
        John Hurley <john.hurley@...ronome.com>,
        oss-drivers@...ronome.com,
        Linux Netdev List <netdev@...r.kernel.org>,
        Alexander Aring <aring@...atatu.com>,
        Roman Mashak <mrv@...atatu.com>,
        Manish Kurup <manish.kurup@...izon.com>
Subject: Re: [PATCH net-next v10 1/3] act_vlan: Change stats update to use
 per-core stats

On Thu, Nov 9, 2017 at 12:45 AM, Manish Kurup <kurup.manish@...il.com> wrote:
> On Wed, Nov 8, 2017 at 9:20 AM, Or Gerlitz <gerlitz.or@...il.com> wrote:
>> On Wed, Nov 8, 2017 at 9:03 PM, Manish Kurup <kurup.manish@...il.com> wrote:

>>> @@ -30,9 +30,10 @@ static int tcf_vlan(struct sk_buff *skb, const struct tc_action *a,
>>>         int err;
>>>         u16 tci;
>>>
>>> -       spin_lock(&v->tcf_lock);
>>>         tcf_lastuse_update(&v->tcf_tm);
>>> -       bstats_update(&v->tcf_bstats, skb);
>>> +       bstats_cpu_update(this_cpu_ptr(v->common.cpu_bstats), skb);
>>> +
>>> +       spin_lock(&v->tcf_lock);
>>>         action = v->tcf_action;
>>

>> before your changes the spin lock also protected the lastuse update call but
>> now it doesn't, why?

> Phase I of my changes, was to get rid of spin_locks, and convert the
> stats to a per-cpu stats model to get better forwarding performance.
> While doing this, I looked at a few 'model TC actions' within
> net/sched (tcf_mirred for example). Neither of them protected the
> tcf_lastuse_update(). I assumed that this was the case because this
> was a 'display-only' field, and as long as it changed to a latest
> timestamp based on packets received, it was OK.

this is really late in the review cycle so lets not stop for that but
if for some  reason there's V11 - would be good to put a comment on
that in the change log