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

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Message-ID: <20190503155528.6of5wl3dq7hdryt7@breakpoint.cc>
Date:   Fri, 3 May 2019 17:55:28 +0200
From:   Florian Westphal <fw@...len.de>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Steffen Klassert <steffen.klassert@...unet.com>,
        Florian Westphal <fw@...len.de>, vakul.garg@....com,
        netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>
Subject: Re: [RFC HACK] xfrm: make state refcounting percpu

Eric Dumazet <eric.dumazet@...il.com> wrote:
 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.

Yes, I understand this.  We'll still still serialize anyway due to
spinlock.

Given Vakul says the state refcount isn't the main problem and Steffen
suggest to insert multiple states instead I don't think working on this
more makes any sense.

Thanks for the pcpu counter infra pointer though, I had not seen it before.