netdev - Re: [PATCH net-next v2 0/4] Implement classifier-action terse dump mode

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Date:   Sun, 17 May 2020 12:13:14 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Davide Caratti <dcaratti@...hat.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next v2 0/4] Implement classifier-action terse dump mode

On Fri, May 15, 2020 at 4:40 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>
> Output rate of current upstream kernel TC filter dump implementation if
> relatively low (~100k rules/sec depending on configuration). This
> constraint impacts performance of software switch implementation that
> rely on TC for their datapath implementation and periodically call TC
> filter dump to update rules stats. Moreover, TC filter dump output a lot
> of static data that don't change during the filter lifecycle (filter
> key, specific action details, etc.) which constitutes significant
> portion of payload on resulting netlink packets and increases amount of
> syscalls necessary to dump all filters on particular Qdisc. In order to
> significantly improve filter dump rate this patch sets implement new
> mode of TC filter dump operation named "terse dump" mode. In this mode
> only parameters necessary to identify the filter (handle, action cookie,
> etc.) and data that can change during filter lifecycle (filter flags,
> action stats, etc.) are preserved in dump output while everything else
> is omitted.
>
> Userspace API is implemented using new TCA_DUMP_FLAGS tlv with only
> available flag value TCA_DUMP_FLAGS_TERSE. Internally, new API requires
> individual classifier support (new tcf_proto_ops->terse_dump()
> callback). Support for action terse dump is implemented in act API and
> don't require changing individual action implementations.

Sorry for being late.

Why terse dump needs a new ops if it only dumps a subset of the
regular dump? That is, why not just pass a boolean flag to regular
->dump() implementation?

I guess that might break user-space ABI? At least some netlink
attributes are not always dumped anyway, so it does not look like
a problem?

Thanks.