netdev - Re: [RFC HACK] xfrm: make state refcounting percpu

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Date:   Fri, 3 May 2019 08:06:05 -0400
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Steffen Klassert <steffen.klassert@...unet.com>,
        Florian Westphal <fw@...len.de>
Cc:     vakul.garg@....com, netdev@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [RFC HACK] xfrm: make state refcounting percpu



On 5/3/19 2:07 AM, Steffen Klassert wrote:
> On Wed, Apr 24, 2019 at 12:40:23PM +0200, Florian Westphal wrote:
>> I'm not sure this is a good idea to begin with, refcount
>> is right next to state spinlock which is taken for both tx and rx ops,
>> plus this complicates debugging quite a bit.
> 
> 


For some reason I have not received Florian response.

Florian, when the percpu counters are in nominal mode,
the updates are only in percpu memory, so the cache line containing struct percpu_ref in the
main object is not dirtied.

(This field/object can be placed in a read-mostly location of the structure if needed)

I would definitely try to use this.