DPDK patches and discussions
 help / color / Atom feed
From: Andrew Rybchenko <arybchenko@solarflare.com>
To: Thomas Monjalon <thomas@monjalon.net>
Cc: Ori Kam <orika@mellanox.com>, "dev@dpdk.org" <dev@dpdk.org>,
	"pbhagavatula@marvell.com" <pbhagavatula@marvell.com>,
	"ferruh.yigit@intel.com" <ferruh.yigit@intel.com>,
	"jerinj@marvell.com" <jerinj@marvell.com>,
	John McNamara <john.mcnamara@intel.com>,
	"Marko Kovacevic" <marko.kovacevic@intel.com>,
	Adrien Mazarguil <adrien.mazarguil@6wind.com>,
	"david.marchand@redhat.com" <david.marchand@redhat.com>,
	"ktraynor@redhat.com" <ktraynor@redhat.com>,
	Olivier Matz <olivier.matz@6wind.com>
Subject: Re: [dpdk-dev] [PATCH 1/2] ethdev: add flow action type update as an offload
Date: Fri, 8 Nov 2019 13:42:23 +0300
Message-ID: <d38c77a7-22ef-7221-feed-69ea5db876a8@solarflare.com> (raw)
In-Reply-To: <1594828.JO7TyvRWtP@xps>

On 11/8/19 1:28 PM, Thomas Monjalon wrote:
> 08/11/2019 09:35, Andrew Rybchenko:
>> The problem:
>> ~~~~~~~~~~~~
>> PMD wants to know before port start if application wants to
>> to use flow MARK/FLAG in the future. It is required because:
>> 1. HW may be configured in a different way to reserve resources
>>    for MARK/FLAG delivery
>> 2. Datapath implementation choice may depend on it (e.g. vPMD
>>    is faster, but does not support MARK)
> Thank you for the clear problem statement.
> I agree with it. This is a real design issue.
>> Discussed solutions:
>> ~~~~~~~~~~~~~~~~~~~~

May be it is not 100% clear since below are alternatives.

>> A. Explicit Rx offload suggested by the patch.
>> B. Implicit by validation of a flow rule with MARK/FLAG actions used.
>> C. Use dynamic field/flag (i.e. application registers dynamic field
>>    and/or flag and PMD uses lookup to solve the problem) plus part
>>    of (B) to discover if a feature is supported.
> The dynamic field should be registered via a new API function
> named '<feature>_init'.
> It means the application must explicit request the feature.
> I agree this is the way to go.

If I understand your statement correctly, but (C) is not ideal since it
looks global. If registered dynamic field of mbuf and is flag that
the feature should be enabled, it is a flag to all ports/devices.

>> All solutions require changes in applications which use these
>> features. There is a deprecation notice in place which advertises
>> DEV_RX_OFFLOAD_FLOW_MARK addition, but may be it is OK to substitute
>> it with solution (B) or (C). Solution (C) requires changes since
>> it should be combined with (B) in order to understand if
>> the feature is supported.
> I don't understand.
> Application request and PMD support are two different things.
> PMD support must be via rte_flow validation on a case by case anyway.

I mean that application wants to understand if the feature is
supported. Then, it wants to enable it. In the case of (B),
if I understand the solution correctly, there is no explicit
way to enable, PMD just detects it because of discovery is done
(that's what I mean by "implicit" and it is a drawback from my
point of view, but still could be considered). (C) solves the
problem of (B).

>> Advantages and drawbacks of solutions:
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> 1. The main drawback of (A) is a "duplication" since we already
>>    have a way to request flow MARK using rte_flow API.
>>    I don't fully agree that it is a duplication, but I agree
>>    that it sounds like duplication and complicates a bit flow
>>    MARK usage by applications. (B) complicates it as well.
>> 2. One more drawback of the solution (A) is the necessity of
>>    similar solution for META and it eats one more offload bit.
>>    Yes, that's true and I think it is not a problem.
>>    It would make it easier for applications to find out if
>>    either MARK or META is supported.
>> 3. The main advantage of the solution (A) is simplicity.
>>    It is simple for application to understand if it supported.
>>    It is simple in PMD to understand that it is required.
>>    It is simple to disable it - just reconfigure.
>>    Also it is easier to document it - just mention that
>>    the offload should be supported and enabled.
>> 4. The main advantage of the solution (B) is no "duplication".
>>    I agree that it is valid argument. Solving the problem
>>    without extra entities is always nice, but unfortunately
>>    it is too complex in this case.
>> 5. The main drawback of the solution (B) is the complexity.
>>    It is necessary to choose a flow rule which should be used
>>    as a criteria. It could be hardware dependent.
>>    Complex logic is require in PMD if it wants to address the
>>    problem and control MARK delivery based on validated flow
>>    rules. It adds dependency between start/stop processing and
>>    flow rules validation code.
>>    It is pretty complicated to document it.
>> 6. Useless enabling of the offload in the case of solution (A)
>>    if really used flow rules do not support MARK looks like
>>    drawback as well, but easily mitigated by a combination
>>    with solution (B) and only required if the application wants
>>    to dive in the level of optimization and complexity and
>>    makes sense if application knows required flow rules in
>>    advance. So, it is not a problem in this case.
>> 7. Solution (C) has drawbacks of the solution (B) for
>>    applications to understand if these features are supported,
>>    but no drawbacks in PMD, since explicit criteria is used to
>>    enable/disable (dynamic field/flag lookup).
>> 8. Solution (C) is nice since it avoids "duplication".
>> 9. The main drawback of the solution (C) is asymmetry.
>>    As it was discussed in the case of RX_TIMESTAMP
>>    (if I remember it correctly):
>>     - PMD advertises RX_TIMESTAMP offload capability
>>     - application enables the offload
>>     - PMD registers dynamic field for timestamp
>>    Solution (C):
>>      - PMD advertises nothing
>>      - application uses solution (B) to understand if
>>        these features are supported
>>      - application registers dynamic field/flag
>>      - PMD does lookup and solve the problem
>>    The asymmetry could be partially mitigated if RX_TIMESTAMP
>>    solution is changed to require an application to register
>>    dynamic fields and PMD to do lookup if the offload is
>>    enabled. So, the only difference will be in no offload
>>    in the case of flow MARK/FLAG and usage of complex logic
>>    to understand if it is supported or no.
>>    May be it would be really good since it will allow to
>>    have dynamic fields registered before mempool population.
>> 10. Common drawback of solutions (B) and (C) is no granularity.
>>     Solution (A) may be per queue while (B) and (C) cannot be
>>     per queue. Moreover (C) looks global - for all devices.
>>     It could be really painful.
>> (C) is nice, but I still vote for simplicity and
>> granularity of (A).
> I vote for clear separation of application needs and PMD support,
> by using the method C (dynamic fields).
> I agree timestamp must use the same path.
> I agree it's complicate because we don't know in advance whether
> a flow rule will be accepted, but that's the reality, config is complex.

Do you think that global nature of the (C) is acceptable?

  reply index

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-25 15:21 pbhagavatula
2019-10-25 15:21 ` [dpdk-dev] [PATCH 2/2] drivers/net: update Rx flow flag and mark capabilities pbhagavatula
2019-10-28 10:50 ` [dpdk-dev] [PATCH 1/2] ethdev: add flow action type update as an offload Ori Kam
2019-10-28 11:53   ` Andrew Rybchenko
2019-10-28 14:00     ` Ori Kam
2019-10-31  9:49       ` Andrew Rybchenko
2019-10-31 14:49         ` Thomas Monjalon
2019-10-31 23:59           ` Zhang, Qi Z
2019-11-01 11:35           ` Andrew Rybchenko
2019-11-03 10:22             ` Ori Kam
2019-11-03 11:41               ` Andrew Rybchenko
2019-11-04 18:37                 ` Ori Kam
2019-11-05  6:50                   ` Andrew Rybchenko
2019-11-05  8:35                     ` Ori Kam
2019-11-05 11:30                       ` Andrew Rybchenko
2019-11-05 16:37                         ` Ori Kam
2019-11-06  6:40                           ` Andrew Rybchenko
2019-11-06  7:42                             ` Ori Kam
2019-11-08  8:35                               ` Andrew Rybchenko
2019-11-08  9:00                                 ` Tom Barbette
2019-11-08 10:28                                 ` Thomas Monjalon
2019-11-08 10:42                                   ` Andrew Rybchenko [this message]
2019-11-08 11:03                                     ` Thomas Monjalon
2019-11-08 11:40                                       ` Zhang, Qi Z
2019-11-08 12:12                                         ` Ori Kam
2019-11-08 12:20                                           ` Andrew Rybchenko
2019-11-08 12:42                                             ` Ori Kam
2019-11-08 13:16                                               ` Zhang, Qi Z
2019-11-08 13:26                                                 ` Thomas Monjalon
2019-11-08 13:06                                         ` Thomas Monjalon
2019-11-08 12:00                                       ` Andrew Rybchenko
2019-11-08 13:17                                         ` Thomas Monjalon
2019-11-08 13:27                                           ` Andrew Rybchenko
2019-11-08 13:30                                             ` Thomas Monjalon
2019-11-19  9:24                                               ` Andrew Rybchenko
2019-11-19  9:50                                                 ` Thomas Monjalon
2019-11-19 10:59                                                   ` Andrew Rybchenko
2019-11-19 11:09                                                     ` Thomas Monjalon
2020-07-03 14:34                                                       ` Ferruh Yigit

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=d38c77a7-22ef-7221-feed-69ea5db876a8@solarflare.com \
    --to=arybchenko@solarflare.com \
    --cc=adrien.mazarguil@6wind.com \
    --cc=david.marchand@redhat.com \
    --cc=dev@dpdk.org \
    --cc=ferruh.yigit@intel.com \
    --cc=jerinj@marvell.com \
    --cc=john.mcnamara@intel.com \
    --cc=ktraynor@redhat.com \
    --cc=marko.kovacevic@intel.com \
    --cc=olivier.matz@6wind.com \
    --cc=orika@mellanox.com \
    --cc=pbhagavatula@marvell.com \
    --cc=thomas@monjalon.net \


* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

DPDK patches and discussions

Archives are clonable:
	git clone --mirror http://inbox.dpdk.org/dev/0 dev/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 dev dev/ http://inbox.dpdk.org/dev \
	public-inbox-index dev

Newsgroup available over NNTP:

AGPL code for this site: git clone https://public-inbox.org/ public-inbox