Re: [dpdk-dev] [PATCH 1/2] [RFC]: ethdev: add pre-defined meter policy API

[Matan Azrad <matan@nvidia.com>]

From: Dumitrescu, Cristian
> Hi Matan,
> 
> > -----Original Message-----
> > From: Matan Azrad <matan@nvidia.com>
> > Sent: Thursday, March 25, 2021 6:57 AM
> > To: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>; Li Zhang
> > <lizh@nvidia.com>; Dekel Peled <dekelp@nvidia.com>; Ori Kam
> > <orika@nvidia.com>; Slava Ovsiienko <viacheslavo@nvidia.com>; Shahaf
> > Shuler <shahafs@nvidia.com>; lironh@marvell.com; Singh, Jasvinder
> > <jasvinder.singh@intel.com>; NBU-Contact-Thomas Monjalon
> > <thomas@monjalon.net>; Yigit, Ferruh <ferruh.yigit@intel.com>; Andrew
> > Rybchenko <andrew.rybchenko@oktetlabs.ru>; Jerin Jacob
> > <jerinjacobk@gmail.com>; Hemant Agrawal <hemant.agrawal@nxp.com>;
> Ajit
> > Khaparde <ajit.khaparde@broadcom.com>
> > Cc: dev@dpdk.org; Raslan Darawsheh <rasland@nvidia.com>; Roni Bar
> > Yanai <roniba@nvidia.com>
> > Subject: RE: [PATCH 1/2] [RFC]: ethdev: add pre-defined meter policy
> > API
> >
> > Hi Cristian
> >
> > Thank you for your important review!
> > I agree with all your comments except one, please see inline.
> >
> > From: Dumitrescu, Cristian
> > > Hi Li and Matan,
> > >
> > > Thank you for your proposal, some comments below.
> > >
> > > I am also adding Jerin and Hemant to this thread, as they also
> > > participated
> > in
> > > the definition of the rte_mtr API in 2017. Also Ajit expressed some
> > > interest
> > in a
> > > previous email.
> > >
> > > > -----Original Message-----
> > > > From: Li Zhang <lizh@nvidia.com>
> > > > Sent: Thursday, March 18, 2021 8:58 AM
> > > > To: dekelp@nvidia.com; orika@nvidia.com; viacheslavo@nvidia.com;
> > > > matan@nvidia.com; shahafs@nvidia.com; lironh@marvell.com; Singh,
> > > > Jasvinder <jasvinder.singh@intel.com>; Thomas Monjalon
> > > > <thomas@monjalon.net>; Yigit, Ferruh <ferruh.yigit@intel.com>;
> > Andrew
> > > > Rybchenko <andrew.rybchenko@oktetlabs.ru>; Dumitrescu, Cristian
> > > > <cristian.dumitrescu@intel.com>
> > > > Cc: dev@dpdk.org; rasland@nvidia.com; roniba@nvidia.com
> > > > Subject: [PATCH 1/2] [RFC]: ethdev: add pre-defined meter policy
> > > > API
> > > >
> > > > Currently, the flow meter policy does not support multiple actions
> > > > per color; also the allowed action types per color are very limited.
> > > > In addition, the policy cannot be pre-defined.
> > > >
> > > > Due to the growing in flow actions offload abilities there is a
> > > > potential for the user to use variety of actions per color differently.
> > > > This new meter policy API comes to allow this potential in the
> > > > most ethdev common way using rte_flow action definition.
> > > > A list of rte_flow actions will be provided by the user per color
> > > > in order to create a meter policy.
> > > > In addition, the API forces to pre-define the policy before the
> > > > meters creation in order to allow sharing of single policy with
> > > > multiple meters efficiently.
> > > >
> > > > meter_policy_id is added into struct rte_mtr_params.
> > > > So that it can get the policy during the meters creation.
> > > >
> > > > Policy id 0 is default policy. Action per color as below:
> > > > green - no action, yellow - no action, red - drop
> > > >
> > > > Allow coloring the packet using a new rte_flow_action_color as
> > > > could be done by the old policy API,
> > > >
> > >
> > > The proposal essentially is to define the meter policy based on
> > > rte_flow
> > actions
> > > rather than a reduced action set defined specifically just for meter object.
> > This
> > > makes sense to me.
> > >
> > > > The next API function were added:
> > > > - rte_mtr_meter_policy_add
> > > > - rte_mtr_meter_policy_delete
> > > > - rte_mtr_meter_policy_update
> > > > - rte_mtr_meter_policy_validate
> > > > The next struct was changed:
> > > > - rte_mtr_params
> > > > - rte_mtr_capabilities
> > > > The next API was deleted:
> > > > - rte_mtr_policer_actions_update
> > > >
> > > > Signed-off-by: Li Zhang <lizh@nvidia.com>
> > > > ---
> > > >  lib/librte_ethdev/rte_flow.h       |  18 ++++
> > > >  lib/librte_ethdev/rte_mtr.c        |  55 ++++++++--
> > > >  lib/librte_ethdev/rte_mtr.h        | 166 ++++++++++++++++++++---------
> > > >  lib/librte_ethdev/rte_mtr_driver.h |  45 ++++++--
> > > >  4 files changed, 210 insertions(
<snip>
> > > > +/**
> > > > + * Policy id 0 is default policy.
> > >
> > > I suggest you do not redundantly specify the value of the default
> > > policy ID
> > in the
> > > comment. Replace by "Default policy ID."
> > >
> > > > + * Action per color as below:
> > > > + * green - no action, yellow - no action, red - drop
> > >
> > > This does not make sense to me as the default policy. The default
> > > policy
> > should
> > > be "no change", i.e. green -> green (no change), yellow -> yellow
> > > (no
> > change),
> > > red -> red (no change).
> >
> > Can you explain why it doesn't make sense to you?
> >
> > Meter with "no change" for all colors has no effect on the packets so
> > it is redundant action which just costs performance and resources -
> > probably never be used.
> >
> 
> The mbuf::sched::color needs to be set for the packet, and the only way to do
> this is by applying the RTE_FLOW_ACTION_TYPE_COLOR Action, right? It would
> make sense that the default policy is to simply apply to the packet the color
> that the meter just computed for the current packet with no change, right?

I don't think so.
When we are working with HW offloads (this is the main goal of rte_flow and this meter API) the motivation is to do the actions directly in the NIC HW.
Moving the color information to the SW is like doing "partial offload".


> > The most common usage for meter is to drop all the packets come above
> > the defined rate limit - so it makes sense to take this behavior as default.
> >
> 
> I don't agree with this assertion either. One typical usage of the color is to
> accept all input packets from the user, either green, yellow or red in the
> absence of any congestion, and charge the user for this traffic; in case of
> congestion, as typically detected later (typically on scheduling and maybe on a
> different network node, depending on the application), the packet color is used
> to prioritize between packets, i.e. drop red packets first before dropping any
> yellow or green packets. In this case, there is no pre-defined "drop all red
> packets straight away" policy.


I familiar with a lot of meter users(at least 5 applications) in the industry, no one use the color actions. 
All of them drop red packets and continue to the next flow actions(after meter) otherwise.


If you insist, we can define 2 default IDs...

> >
> > > I suggest we avoid the "no action" statement, as it might be confusing.
> >
> > Maybe "do nothing" is better?
> >
> 
> Yes, makes sense to me.

<snip>