doc: flow rule removal on port stop

  There is a discrepancy between RTE ETHDEV API and flow rules guide
regarding flow rules maintenance after port stop.  RTE ETHDEV API in
librte_ethdev.h declares that flow rules will not be stored in PMD
after port stop:
 >>>>> Quite start
 Please note that some configuration is not stored between calls to
 rte_eth_dev_stop()/rte_eth_dev_start(). The following configuration
 will be retained:

 - MTU
 - flow control settings
 - receive mode configuration (promiscuous mode, all-multicast mode,
   hardware checksum mode, RSS/VMDQ settings etc.)
 - VLAN filtering configuration
 - default MAC address
 - MAC addresses supplied to MAC address array
 - flow director filtering mode (but not filtering rules)
 - NIC queue statistics mappings
 <<<< Quote end

PMD cannot always correctly restore flow rules after port stop / port
start because application may alter port configuration after port stop
without PMD knowledge about undergoing changes.  Consider the
following scenario:
application configures 2 queues 0 and 1 and creates a flow rule with
'queue index 1' action. After that application stops the port and
removes queue 1.
Although PMD can implement flow rule shadow copy to be used for
restore after port start, attempt to restore flow rule from shadow
will fail in example above and PMD could not notify application about
that failure.  As the result, flow rules map in HW will differ from
what application expects.  In addition, flow rules shadow copy used
for port start restore consumes considerable amount of system memory,
especially in systems with millions of flow rules.

Signed-off-by: Gregory Etelson <getelson@nvidia.com>
Acked-by: Ori Kam <orika@nvidia.com>
---
 doc/guides/prog_guide/rte_flow.rst | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
  

On 11/17/20 10:18 PM, Gregory Etelson wrote:
> There is a discrepancy between RTE ETHDEV API and flow rules guide
> regarding flow rules maintenance after port stop.  RTE ETHDEV API in
> librte_ethdev.h declares that flow rules will not be stored in PMD
> after port stop:
>   >>>>> Quite start
>   Please note that some configuration is not stored between calls to
>   rte_eth_dev_stop()/rte_eth_dev_start(). The following configuration
>   will be retained:
> 
>   - MTU
>   - flow control settings
>   - receive mode configuration (promiscuous mode, all-multicast mode,
>     hardware checksum mode, RSS/VMDQ settings etc.)
>   - VLAN filtering configuration
>   - default MAC address
>   - MAC addresses supplied to MAC address array
>   - flow director filtering mode (but not filtering rules)
>   - NIC queue statistics mappings
>   <<<< Quote end
> 
> PMD cannot always correctly restore flow rules after port stop / port
> start because application may alter port configuration after port stop
> without PMD knowledge about undergoing changes.  Consider the
> following scenario:
> application configures 2 queues 0 and 1 and creates a flow rule with
> 'queue index 1' action. After that application stops the port and
> removes queue 1.
> Although PMD can implement flow rule shadow copy to be used for
> restore after port start, attempt to restore flow rule from shadow
> will fail in example above and PMD could not notify application about
> that failure.  As the result, flow rules map in HW will differ from
> what application expects.  In addition, flow rules shadow copy used
> for port start restore consumes considerable amount of system memory,
> especially in systems with millions of flow rules.
> 
> Signed-off-by: Gregory Etelson <getelson@nvidia.com>
> Acked-by: Ori Kam <orika@nvidia.com>
> ---
>   doc/guides/prog_guide/rte_flow.rst | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/guides/prog_guide/rte_flow.rst b/doc/guides/prog_guide/rte_flow.rst
> index 944e8242d6..dfe5a40f8e 100644
> --- a/doc/guides/prog_guide/rte_flow.rst
> +++ b/doc/guides/prog_guide/rte_flow.rst
> @@ -3055,10 +3055,9 @@ Caveats
>     temporarily replacing the burst function pointers), an appropriate error
>     code must be returned (``EBUSY``).
>   
> -- PMDs, not applications, are responsible for maintaining flow rules
> +- Applications, not PMDs, are responsible for maintaining flow rules
>     configuration when stopping and restarting a port or performing other
> -  actions which may affect them. They can only be destroyed explicitly by
> -  applications.
> +  actions which may affect them.
>   
>   For devices exposing multiple ports sharing global settings affected by flow
>   rules:
> 

Re-reading it, it still looks vague. What happens on:
  - port stop without removal of flow rule before
  - port close without removal of flow rules before
  - port reset (which could be stop/start, e.g. to recover from error 
condition)
  

Hello Andrew,

> On 11/17/20 10:18 PM, Gregory Etelson wrote:
> > There is a discrepancy between RTE ETHDEV API and flow rules guide
> > regarding flow rules maintenance after port stop.  RTE ETHDEV API in
> > librte_ethdev.h declares that flow rules will not be stored in PMD
> > after port stop:
> >   >>>>> Quite start
> >   Please note that some configuration is not stored between calls to
> >   rte_eth_dev_stop()/rte_eth_dev_start(). The following configuration
> >   will be retained:
> >
> >   - MTU
> >   - flow control settings
> >   - receive mode configuration (promiscuous mode, all-multicast mode,
> >     hardware checksum mode, RSS/VMDQ settings etc.)
> >   - VLAN filtering configuration
> >   - default MAC address
> >   - MAC addresses supplied to MAC address array
> >   - flow director filtering mode (but not filtering rules)
> >   - NIC queue statistics mappings
> >   <<<< Quote end
> >
> > PMD cannot always correctly restore flow rules after port stop / port
> > start because application may alter port configuration after port stop
> > without PMD knowledge about undergoing changes.  Consider the
> > following scenario:
> > application configures 2 queues 0 and 1 and creates a flow rule with
> > 'queue index 1' action. After that application stops the port and
> > removes queue 1.
> > Although PMD can implement flow rule shadow copy to be used for
> > restore after port start, attempt to restore flow rule from shadow
> > will fail in example above and PMD could not notify application about
> > that failure.  As the result, flow rules map in HW will differ from
> > what application expects.  In addition, flow rules shadow copy used
> > for port start restore consumes considerable amount of system memory,
> > especially in systems with millions of flow rules.
> >
> > Signed-off-by: Gregory Etelson <getelson@nvidia.com>
> > Acked-by: Ori Kam <orika@nvidia.com>
> > ---
> >   doc/guides/prog_guide/rte_flow.rst | 5 ++---
> >   1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/doc/guides/prog_guide/rte_flow.rst
> > b/doc/guides/prog_guide/rte_flow.rst
> > index 944e8242d6..dfe5a40f8e 100644
> > --- a/doc/guides/prog_guide/rte_flow.rst
> > +++ b/doc/guides/prog_guide/rte_flow.rst
> > @@ -3055,10 +3055,9 @@ Caveats
> >     temporarily replacing the burst function pointers), an appropriate
> error
> >     code must be returned (``EBUSY``).
> >
> > -- PMDs, not applications, are responsible for maintaining flow rules
> > +- Applications, not PMDs, are responsible for maintaining flow rules
> >     configuration when stopping and restarting a port or performing
> > other
> > -  actions which may affect them. They can only be destroyed
> > explicitly by
> > -  applications.
> > +  actions which may affect them.
> >
> >   For devices exposing multiple ports sharing global settings affected
> by flow
> >   rules:
> >
> 
> Re-reading it, it still looks vague. What happens on:
>   - port stop without removal of flow rule before
>   - port close without removal of flow rules before
>   - port reset (which could be stop/start, e.g. to recover from error
> condition)

PMD should remove all flows related to hardware resource that was invalidated.
  

On 11/18/20 11:59 AM, Gregory Etelson wrote:
> Hello Andrew,
> 
>> On 11/17/20 10:18 PM, Gregory Etelson wrote:
>>> There is a discrepancy between RTE ETHDEV API and flow rules guide
>>> regarding flow rules maintenance after port stop.  RTE ETHDEV API in
>>> librte_ethdev.h declares that flow rules will not be stored in PMD
>>> after port stop:
>>>   >>>>> Quite start
>>>   Please note that some configuration is not stored between calls to
>>>   rte_eth_dev_stop()/rte_eth_dev_start(). The following configuration
>>>   will be retained:
>>>
>>>   - MTU
>>>   - flow control settings
>>>   - receive mode configuration (promiscuous mode, all-multicast mode,
>>>     hardware checksum mode, RSS/VMDQ settings etc.)
>>>   - VLAN filtering configuration
>>>   - default MAC address
>>>   - MAC addresses supplied to MAC address array
>>>   - flow director filtering mode (but not filtering rules)
>>>   - NIC queue statistics mappings
>>>   <<<< Quote end
>>>
>>> PMD cannot always correctly restore flow rules after port stop / port
>>> start because application may alter port configuration after port stop
>>> without PMD knowledge about undergoing changes.  Consider the
>>> following scenario:
>>> application configures 2 queues 0 and 1 and creates a flow rule with
>>> 'queue index 1' action. After that application stops the port and
>>> removes queue 1.
>>> Although PMD can implement flow rule shadow copy to be used for
>>> restore after port start, attempt to restore flow rule from shadow
>>> will fail in example above and PMD could not notify application about
>>> that failure.  As the result, flow rules map in HW will differ from
>>> what application expects.  In addition, flow rules shadow copy used
>>> for port start restore consumes considerable amount of system memory,
>>> especially in systems with millions of flow rules.
>>>
>>> Signed-off-by: Gregory Etelson <getelson@nvidia.com>
>>> Acked-by: Ori Kam <orika@nvidia.com>
>>> ---
>>>   doc/guides/prog_guide/rte_flow.rst | 5 ++---
>>>   1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/doc/guides/prog_guide/rte_flow.rst
>>> b/doc/guides/prog_guide/rte_flow.rst
>>> index 944e8242d6..dfe5a40f8e 100644
>>> --- a/doc/guides/prog_guide/rte_flow.rst
>>> +++ b/doc/guides/prog_guide/rte_flow.rst
>>> @@ -3055,10 +3055,9 @@ Caveats
>>>     temporarily replacing the burst function pointers), an appropriate
>> error
>>>     code must be returned (``EBUSY``).
>>>
>>> -- PMDs, not applications, are responsible for maintaining flow rules
>>> +- Applications, not PMDs, are responsible for maintaining flow rules
>>>     configuration when stopping and restarting a port or performing
>>> other
>>> -  actions which may affect them. They can only be destroyed
>>> explicitly by
>>> -  applications.
>>> +  actions which may affect them.
>>>
>>>   For devices exposing multiple ports sharing global settings affected
>> by flow
>>>   rules:
>>>
>>
>> Re-reading it, it still looks vague. What happens on:
>>   - port stop without removal of flow rule before
>>   - port close without removal of flow rules before
>>   - port reset (which could be stop/start, e.g. to recover from error
>> condition)
> 
> PMD should remove all flows related to hardware resource that was invalidated.

Stop? Close? I agree and documentation should say so in a bit
clear way.
  

> >> On 11/17/20 10:18 PM, Gregory Etelson wrote:
> >>> There is a discrepancy between RTE ETHDEV API and flow rules guide
> >>> regarding flow rules maintenance after port stop.  RTE ETHDEV API in
> >>> librte_ethdev.h declares that flow rules will not be stored in PMD
> >>> after port stop:
> >>>   >>>>> Quite start
> >>>   Please note that some configuration is not stored between calls to
> >>>   rte_eth_dev_stop()/rte_eth_dev_start(). The following configuration
> >>>   will be retained:
> >>>
> >>>   - MTU
> >>>   - flow control settings
> >>>   - receive mode configuration (promiscuous mode, all-multicast mode,
> >>>     hardware checksum mode, RSS/VMDQ settings etc.)
> >>>   - VLAN filtering configuration
> >>>   - default MAC address
> >>>   - MAC addresses supplied to MAC address array
> >>>   - flow director filtering mode (but not filtering rules)
> >>>   - NIC queue statistics mappings
> >>>   <<<< Quote end
> >>>
> >>> PMD cannot always correctly restore flow rules after port stop /
> >>> port start because application may alter port configuration after
> >>> port stop without PMD knowledge about undergoing changes.  Consider
> >>> the following scenario:
> >>> application configures 2 queues 0 and 1 and creates a flow rule with
> >>> 'queue index 1' action. After that application stops the port and
> >>> removes queue 1.
> >>> Although PMD can implement flow rule shadow copy to be used for
> >>> restore after port start, attempt to restore flow rule from shadow
> >>> will fail in example above and PMD could not notify application
> >>> about that failure.  As the result, flow rules map in HW will differ
> >>> from what application expects.  In addition, flow rules shadow copy
> >>> used for port start restore consumes considerable amount of system
> >>> memory, especially in systems with millions of flow rules.
> >>>
> >>> Signed-off-by: Gregory Etelson <getelson@nvidia.com>
> >>> Acked-by: Ori Kam <orika@nvidia.com>
> >>> ---
> >>>   doc/guides/prog_guide/rte_flow.rst | 5 ++---
> >>>   1 file changed, 2 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/doc/guides/prog_guide/rte_flow.rst
> >>> b/doc/guides/prog_guide/rte_flow.rst
> >>> index 944e8242d6..dfe5a40f8e 100644
> >>> --- a/doc/guides/prog_guide/rte_flow.rst
> >>> +++ b/doc/guides/prog_guide/rte_flow.rst
> >>> @@ -3055,10 +3055,9 @@ Caveats
> >>>     temporarily replacing the burst function pointers), an
> >>> appropriate
> >> error
> >>>     code must be returned (``EBUSY``).
> >>>
> >>> -- PMDs, not applications, are responsible for maintaining flow
> >>> rules
> >>> +- Applications, not PMDs, are responsible for maintaining flow
> >>> +rules
> >>>     configuration when stopping and restarting a port or performing
> >>> other
> >>> -  actions which may affect them. They can only be destroyed
> >>> explicitly by
> >>> -  applications.
> >>> +  actions which may affect them.
> >>>
> >>>   For devices exposing multiple ports sharing global settings
> >>> affected
> >> by flow
> >>>   rules:
> >>>
> >>
> >> Re-reading it, it still looks vague. What happens on:
> >>   - port stop without removal of flow rule before
> >>   - port close without removal of flow rules before
> >>   - port reset (which could be stop/start, e.g. to recover from error
> >> condition)
> >
> > PMD should remove all flows related to hardware resource that was
> invalidated.
> 
> Stop? Close? I agree and documentation should say so in a bit clear way.

I'll post updated document patch.