netdev - Re: [Patch net] net: saving irq context for peernet2id()

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Date:   Sat, 22 Oct 2016 15:02:56 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Stephen Smalley <sds@...ho.nsa.gov>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Elad Raz <e@...draz.com>, Richard Guy Briggs <rgb@...hat.com>
Subject: Re: [Patch net] net: saving irq context for peernet2id()

On Fri, Oct 21, 2016 at 11:26 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Fri, Oct 21, 2016 at 1:03 PM, Paul Moore <paul@...l-moore.com> wrote:
>> On Fri, Oct 21, 2016 at 2:02 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>> On Fri, Oct 21, 2016 at 9:19 AM, Paul Moore <paul@...l-moore.com> wrote:
>>>> On Thu, Oct 20, 2016 at 7:35 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>>>> This is what I did in the follow up patch. I attach the updated version
>>>>> in this email for you to review ...
>>>>
>>>> I think there is still some confusion.  The second patch you posted
>>>> still has two queues with potentially duplicated (minus the length
>>>> tweaks) skbs.
>>>
>>> The current code without my patch is already this, the only difference
>>> is there is no queue for multicast case, duplication is already there.
>>
>> The difference is the period of time where the skbs are duplicated.
>> You patch duplicates the skb and then queues them, I'm suggesting
>> putting a single skb in the queue and then only duplicating it once it
>> has been pulled off the queue.
>
> I never disagree, the only thing you never explain is why we must do
> it in this patch rather than a patch later?

It seems obvious: if you do the skb_copy() before you queue the skbs
you are doubling the amount of memory used which is undesirable.

-- 
paul moore
www.paul-moore.com