Date:   Mon, 19 Nov 2018 11:04:28 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>,
        "Chopra, Manish" <Manish.Chopra@...ium.com>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "Elior, Ariel" <Ariel.Elior@...ium.com>,
        "michael.chan@...adcom.com" <michael.chan@...adcom.com>,
        "santosh@...lsio.com" <santosh@...lsio.com>,
        "madalin.bucur@....com" <madalin.bucur@....com>,
        "yisen.zhuang@...wei.com" <yisen.zhuang@...wei.com>,
        "salil.mehta@...wei.com" <salil.mehta@...wei.com>,
        "jeffrey.t.kirsher@...el.com" <jeffrey.t.kirsher@...el.com>,
        "tariqt@...lanox.com" <tariqt@...lanox.com>,
        "saeedm@...lanox.com" <saeedm@...lanox.com>,
        "jiri@...lanox.com" <jiri@...lanox.com>,
        "idosch@...lanox.com" <idosch@...lanox.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
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        "andrew@...n.ch" <andrew@...n.ch>,
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        <vivien.didelot@...oirfairelinux.com>,
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        "joabreu@...opsys.com" <joabreu@...opsys.com>,
        "linux-net-drivers@...arflare.com" <linux-net-drivers@...arflare.com>,
        "ganeshgr@...lsio.com" <ganeshgr@...lsio.com>
Subject: Re: [PATCH 00/10] add flow_rule infrastructure

On 11/19/18 1:57 AM, Jiri Pirko wrote:
> Mon, Nov 19, 2018 at 10:19:28AM CET, Manish.Chopra@...ium.com wrote:
>>> -----Original Message-----
>>> From: netdev-owner@...r.kernel.org <netdev-owner@...r.kernel.org> On
>>> Behalf Of Pablo Neira Ayuso
>>> Sent: Friday, November 16, 2018 7:11 AM
>>> To: netdev@...r.kernel.org
>>> Cc: davem@...emloft.net; thomas.lendacky@....com;
>>> f.fainelli@...il.com; Elior, Ariel <Ariel.Elior@...ium.com>;
>>> michael.chan@...adcom.com; santosh@...lsio.com;
>>> madalin.bucur@....com; yisen.zhuang@...wei.com;
>>> salil.mehta@...wei.com; jeffrey.t.kirsher@...el.com; tariqt@...lanox.com;
>>> saeedm@...lanox.com; jiri@...lanox.com; idosch@...lanox.com;
>>> jakub.kicinski@...ronome.com; peppe.cavallaro@...com;
>>> grygorii.strashko@...com; andrew@...n.ch;
>>> vivien.didelot@...oirfairelinux.com; alexandre.torgue@...com;
>>> joabreu@...opsys.com; linux-net-drivers@...arflare.com;
>>> ganeshgr@...lsio.com
>>> Subject: [PATCH 00/10] add flow_rule infrastructure
>>>
>>> External Email
>>>
>>> This patchset introduces a kernel intermediate representation (IR) to express
>>> ACL hardware offloads, this is heavily based on the existing flow dissector
>>> infrastructure and the TC actions. This IR can be used by different frontend
>>> ACL interfaces such as ethtool_rxnfc and tc to represent ACL hardware
>>> offloads. Main goal is to simplify the development of ACL hardware offloads
>>> for the existing frontend interfaces, the idea is that driver developers do not
>>> need to add one specific parser for each ACL frontend, instead each frontend
>>> can just generate this flow_rule IR and pass it to drivers to populate the
>>> hardware IR.
>>>
>>>                 .   ethtool_rxnfc   tc
>>>                |       (ioctl)    (netlink)
>>>                |          |         |     translate native
>>>       Frontend |          |         |  interface representation
>>>                |          |         |      to flow_rule IR
>>>                |          |         |
>>>                 .         \/        \/
>>>                 .         flow_rule IR
>>>                |                |
>>>        Drivers |                | parsing of flow_rule IR
>>>                |                |  to populate hardware IR
>>>                |               \/
>>>                 .      hardware IR (driver)
>>>
>>> For design and implementation details, please have a look at:
>>>
>>>         https://lwn.net/Articles/766695/
>>>
>>> As an example, with this patchset, it should be possible to simplify the
>>> existing net/qede driver which already has two parsers to populate the
>>> hardware IR, one for ethtool_rxnfc interface and another for tc.
>>>
>>> This batch is composed of 10 patches:
>>>
>>> Patch #1 adds the flow_match structure, this includes the
>>>          flow_rule_match_key() interface to check for existing selectors
>>>          that are in used in the rule and the flow_rule_match_*()
>>>          functions to fetch the selector value and the mask. This
>>>          also introduces the initial flow_rule structure skeleton to
>>>          avoid a follow up patch that would update the same LoCs.
>>>
>>> Patch #2 makes changes to packet edit parser of mlx5e driver, to prepare
>>>          introduction of the new flow_action to mangle packets.
>>>
>>> Patch #3 Introduce flow_action infrastructure. This infrastructure is
>>>          based on the TC actions. Patch #8 extends it so it also
>>>          supports two new actions that are only available through the
>>>          ethtool_rxnfc interface.
>>>
>>> Patch #4 Add function to translate TC action to flow_action from
>>>          cls_flower.
>>>
>>> Patch #5 Add infrastructure to fetch statistics into container structure
>>>          and synchronize them to TC actions from cls_flower. Another
>>>          preparation patch before patch #7, so we can stop exposing the
>>>          TC action native layout to the drivers.
>>>
>>> Patch #6 Use flow_action infrastructure from drivers.
>>>
>>> Patch #7 Do not expose TC actions to drivers anymore, now that drivers
>>>          have been converted to use the flow_action infrastructure after
>>>          patch #5.
>>>
>>> Patch #8 Support to wake-up-on-lan and queue actions for the flow_action
>>>          infrastructure, two actions supported by NICs. This is used by
>>>          the ethtool_rx_flow interface.
>>>
>>> Patch #9 Add a function to translate from ethtool_rx_flow_spec structure
>>>          to the flow_action structure. This is a simple enough for its
>>>          first client: the ethtool_rxnfc interface in the bcm_sf2 driver.
>>>
>>> Patch #10 Update bcm_sf2 to use this new translator function and
>>>           update codebase to configure hardware IR using the
>>>           flow_action representation. This will allow later development
>>>           of cls_flower using the same codebase from the driver.
>>>
>>> This patchset has passed here functional tests of the codepath that generates
>>> the flow_rule structure and the functions to implement the parsers that
>>> populate the hardware IR.
>>>
>>> Thanks.
>>>
>>> Pablo Neira Ayuso (10):
>>>   flow_dissector: add flow_rule and flow_match structures and use them
>>>   net/mlx5e: support for two independent packet edit actions
>>>   flow_dissector: add flow action infrastructure
>>>   cls_api: add translator to flow_action representation
>>>   cls_flower: add statistics retrieval infrastructure and use it
>>>   drivers: net: use flow action infrastructure
>>>   cls_flower: don't expose TC actions to drivers anymore
>>>   flow_dissector: add wake-up-on-lan and queue to flow_action
>>>   flow_dissector: add basic ethtool_rx_flow_spec to flow_rule structure
>>> translator
>>>   dsa: bcm_sf2: use flow_rule infrastructure
>>>
>>>  drivers/net/dsa/bcm_sf2_cfp.c                      | 103 ++-
>>>  drivers/net/ethernet/broadcom/bnxt/bnxt_tc.c       | 252 +++----
>>>  .../net/ethernet/chelsio/cxgb4/cxgb4_tc_flower.c   | 450 ++++++-------
>>>  drivers/net/ethernet/intel/i40e/i40e_main.c        | 178 ++---
>>>  drivers/net/ethernet/intel/iavf/iavf_main.c        | 195 +++---
>>>  drivers/net/ethernet/intel/igb/igb_main.c          |  64 +-
>>>  drivers/net/ethernet/mellanox/mlx5/core/en_tc.c    | 743 ++++++++++--------
>>> ---
>>>  drivers/net/ethernet/mellanox/mlxsw/spectrum_acl.c |   2 +-
>>>  .../net/ethernet/mellanox/mlxsw/spectrum_flower.c  | 259 ++++---
>>> drivers/net/ethernet/netronome/nfp/flower/action.c | 196 +++---
>>> drivers/net/ethernet/netronome/nfp/flower/match.c  | 416 ++++++------
>>>  .../net/ethernet/netronome/nfp/flower/offload.c    | 151 ++---
>>>  drivers/net/ethernet/qlogic/qede/qede_filter.c     |  93 ++-
>>>  include/net/flow_dissector.h                       | 185 +++++
>>>  include/net/pkt_cls.h                              |  23 +-
>>>  net/core/flow_dissector.c                          | 341 ++++++++++
>>>  net/sched/cls_api.c                                | 113 ++++
>>>  net/sched/cls_flower.c                             |  42 +-
>>>  18 files changed, 2120 insertions(+), 1686 deletions(-)
>>>
>>> --
>>> 2.11.0
>>
>> Today, we have different kernel interfaces(aRFS/ethtool/tc) to do flow offloading.
>> One big question arises in my mind that why we need these all different interfaces to do flow offloading and
>> why can't they just be combined into a single kernel interface somehow.
>> Having these flow offloading done through various hooks makes driver implementation really complex.
>>
>> Specially when looking at ethtool/tc flows most of the use cases seems common to me -
>>
>> 1.  Drop action can be done on tuples from both tc/ethtool flows.
>> 2.  Flow redirection is done from both ethtool/tc
>>     (May be with just slight difference ? as Ethtool does steering on PF and VF/VF-queues
>>      but tc doesn't have redirection on queues which can be extended over tc)

We discussed several times before with Jiri at various conferences, and
I unfortunately don't have the time to look into doing it, but if
cls_flower gained support for ethtool_rx_flow_spec::location, we should
be good in terms of feature parity. Pablo also identified the
RX_CLS_FLOW_WAKE as something that needs to be supported, but this is a
simple thing that could be implemented as a special tc action (should?)

>> 3.  Could be more such common cases which could be the reason to combine them through single interface ?

Main reason IMHO for going to an unified interface is that ultimately
the piece of HW that implements filtering/action is shared across all
programming interfaces. If they all have about roughly the same feature
set, yet some slight feature deviation or semantic differences, this
gets confusing for driver writers and users.

> 
> Sure you can make one interface feature complete. But that does not mean
> you can remove the others. At least not easily. You woul break UAPI.

Indeed, though we can have a couple of strategies to unify and later
deprecate them:

1) Go after each application and make them use the chosen interface,
e.g: the tc/cls_flower UAPI, this does not really scale well because
while we can easily get mainstream reference applications converted such
as ethtool, iptables, xtables, we don't know what people have designed
around the UAPI interface, and usually this also does not mean bindings
to different languages (e.g: ethtool python) would be converted. Because
we have the application converted to the native interface, there is no
loss in translation or performance penalty from going to the kernel's IR.

2) We convert the non-chosen interfaces (e.g: ethtool, *tables) from
within the kernel through the chosen IR and programming interface, that
way we can easily identify which applications are still using the
deprecated interface and issue an appropriate warning in kernel version
XZY for instance. The drawback is that you have a translation so that
could mean loss of information and/or performance penalty if rule
insertion/deletion is a hot path (which is unfortunately likely the case).
-- 
Florian

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