netdev - Re: [PATCH net-next 06/11] netfilter: nf_flow_table: count and limit hw offloaded entries

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Date:   Thu, 19 May 2022 16:11:36 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     netfilter-devel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org, pabeni@...hat.com,
        Felix Fietkau <nbd@....name>
Subject: Re: [PATCH net-next 06/11] netfilter: nf_flow_table: count and
 limit hw offloaded entries

On Fri, 20 May 2022 00:02:01 +0200 Pablo Neira Ayuso wrote:
> To improve hardware offload debuggability and scalability introduce
> 'nf_flowtable_count_hw' and 'nf_flowtable_max_hw' sysctl entries in new
> dedicated 'net/netfilter/ft' namespace. Add new pernet struct nf_ft_net in
> order to store the counter and sysctl header of new sysctl table.
> 
> Count the offloaded flows in workqueue add task handler. Verify that
> offloaded flow total is lower than allowed maximum before calling the
> driver callbacks. To prevent spamming the 'add' workqueue with tasks when
> flows can't be offloaded anymore also check that count is below limit
> before queuing offload work. This doesn't prevent all redundant workqueue
> task since counter can be taken by concurrent work handler after the check
> had been performed but before the offload job is executed but it still
> greatly reduces such occurrences. Note that flows that were not offloaded
> due to counter being larger than the cap can still be offloaded via refresh
> function.
> 
> Ensure that flows are accounted correctly by verifying IPS_HW_OFFLOAD_BIT
> value before counting them. This ensures that add/refresh code path
> increments the counter exactly once per flow when setting the bit and
> decrements it only for accounted flows when deleting the flow with the bit
> set.

Why a sysctl and not a netlink attr per table or per device?