netdev - Re: [PATCH net-next] netfilter: nft_counter: rework atomic dump and reset

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Date:   Sun, 11 Dec 2016 16:13:49 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     netfilter-devel@...r.kernel.org, eric.dumazet@...il.com,
        netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH net-next] netfilter: nft_counter: rework atomic dump and reset

On Sunday, December 11, 2016 11:43:59 AM CET Pablo Neira Ayuso wrote:
> Dump and reset doesn't work unless cmpxchg64() is used both from packet
> and control plane paths. This approach is going to be slow though.
> Instead, use a percpu seqcount to fetch counters consistently, then
> subtract bytes and packets in case a reset was requested.
> 
> The cpu that running over the reset code is guaranteed to own this stats
> exclusively, we have to turn counters into signed 64bit though so stats
> update on reset don't get wrong on underflow.
> 
> This patch is based on original sketch from Eric Dumazet.
> 
> Fixes: 43da04a593d8 ("netfilter: nf_tables: atomic dump and reset for stateful objects")
> Suggested-by: Eric Dumazet <eric.dumazet@...il.com>
> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
> 

Looks great, I had a similar idea that I was going to suggest the
other day, but yours is better anyway.

	Arnd