Re: [ovs-discuss] OVS megaflows

[Sara Gittlin]

I took a look  at the datapath code -  saw only single table, which
its entries are microflows and megaflows
the megaflows are indicated by non-zero mask fields
Sara


On Wed, Aug 16, 2017 at 9:59 AM, Sara Gittlin  wrote:
> Thank you Joe
> Few questions:
> 1. Are there 2 separate flow tables in the kernel data-path ? for
> microflows and megaflows ?
>
> 2. If the answer is yes :
>- When pkt arrives,  is it first checked against the microflows
> table and if there is no  match, then it checked against the megaflows
> table ?
>
>- Then if the pkt matches a megaflow - a new microflow will be
> generated by the kernel for this pkt ?  this make sense to improve
> performance.
>
>
> Sara
>
>
> On Tue, Aug 15, 2017 at 7:16 PM, Joe Stringer  wrote:
>> On the first point - it's a little more subtle than that. A traffic
>> flow (eg, a connection) must arrive at OVS, the first packet is sent
>> through userspace, which causes userspace to install a megaflow into
>> the datapath. Subsequently, if any traffic which matches that megaflow
>> arrives, it will directly 'hit' the megaflow entry and execute the
>> associated actions without going to userspace. Typically we use
>> "microflow" to refer to a packet headers description which
>> exact-matches all known fields, while "megaflow" allows a mask to be
>> applied in addition to this, which allows the traffic which would
>> otherwise be handled by multiple microflows to instead be handled by a
>> single megaflow. There is no dependency between megaflows and
>> microflows.
>>
>> Cheers,
>> Joe
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Re: [ovs-discuss] OVS megaflows

[Sara Gittlin]

Thank you Joe
Few questions:
1. Are there 2 separate flow tables in the kernel data-path ? for
microflows and megaflows ?

2. If the answer is yes :
   - When pkt arrives,  is it first checked against the microflows
table and if there is no  match, then it checked against the megaflows
table ?

   - Then if the pkt matches a megaflow - a new microflow will be
generated by the kernel for this pkt ?  this make sense to improve
performance.


Sara


On Tue, Aug 15, 2017 at 7:16 PM, Joe Stringer  wrote:
> On the first point - it's a little more subtle than that. A traffic
> flow (eg, a connection) must arrive at OVS, the first packet is sent
> through userspace, which causes userspace to install a megaflow into
> the datapath. Subsequently, if any traffic which matches that megaflow
> arrives, it will directly 'hit' the megaflow entry and execute the
> associated actions without going to userspace. Typically we use
> "microflow" to refer to a packet headers description which
> exact-matches all known fields, while "megaflow" allows a mask to be
> applied in addition to this, which allows the traffic which would
> otherwise be handled by multiple microflows to instead be handled by a
> single megaflow. There is no dependency between megaflows and
> microflows.
>
> Cheers,
> Joe
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Re: [ovs-discuss] OVS megaflows

[Joe Stringer]

On the first point - it's a little more subtle than that. A traffic
flow (eg, a connection) must arrive at OVS, the first packet is sent
through userspace, which causes userspace to install a megaflow into
the datapath. Subsequently, if any traffic which matches that megaflow
arrives, it will directly 'hit' the megaflow entry and execute the
associated actions without going to userspace. Typically we use
"microflow" to refer to a packet headers description which
exact-matches all known fields, while "megaflow" allows a mask to be
applied in addition to this, which allows the traffic which would
otherwise be handled by multiple microflows to instead be handled by a
single megaflow. There is no dependency between megaflows and
microflows.

Cheers,
Joe
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Re: [ovs-discuss] OVS megaflows

[Sara Gittlin]

Can i summarize:
1. Once N microflows are installed in the kernel cache:
we can install a megaflow/s in kernel datapath,  if it possible to
generate a megaflow/s for them
2. These megaflow/s remain in the kernel megaflow cache as long as the
associated flows are in userspace openflow tables, regardless of
 microflows eviction from kernel cache.
Thanks in advance
Sara


On Mon, Aug 14, 2017 at 8:47 PM, Joe Stringer  wrote:
> The FAQ is referring to megaflows as well, the reasons are the same.
> Neither microflows nor megaflows can be pre-populated.
>
> On 14 August 2017 at 00:35, Sara Gittlin  wrote:
>> I  understand that this citation refers to the kernel microflows  tables.
>> the kernel megaflows table *can be* pre-populated. Correct ?
>> Sara
>>
>> On Mon, Aug 14, 2017 at 9:31 AM, Sara Gittlin  wrote:
>>> Thanks you Joe
>>> the following citation is in a contradiction to the idea of
>>> pre-populating megaflows in kernel datapath .
>>> this is from  http://docs.openvswitch.org/en/latest/faq/design/
>>>
>>> "Q: Can OVS populate the kernel flow table in advance instead of in
>>> reaction to packets?
>>>
>>> A: No. There are several reasons:
>>>
>>> Kernel flows are not as sophisticated as OpenFlow flows, which means
>>> that some OpenFlow policies could require a large number of kernel
>>> flows. The “conjunctive match” feature is an extreme example: the
>>> number of kernel flows it requires is the product of the number of
>>> flows in each dimension.
>>> With multiple OpenFlow flow tables and simple sets of actions, the
>>> number of kernel flows required can be as large as the product of the
>>> number of flows in each dimension. With more sophisticated actions,
>>> the number of kernel flows could be even larger.
>>> Open vSwitch is designed so that any version of OVS userspace
>>> interoperates with any version of the OVS kernel module. This forward
>>> and backward compatibility requires that userspace observe how the
>>> kernel module parses received packets. This is only possible in a
>>> straightforward way when userspace adds kernel flows in reaction to
>>> received packets."
>>>
>>> Thanks in advance - Sara
>>>
>>> On Mon, Jul 24, 2017 at 10:58 PM, Joe Stringer  wrote:
 On 23 July 2017 at 06:37, Sara Gittlin  wrote:
> Hello,
> I understand that there is a support for megaflows in the kernel and 
> netlink.
> I also understand that there is no megaflow implementation in ofproto.
> i.e. there is no implementation of compressing (if possible) all flows
> in ofproto table to megaflows and installing it in the datapath. is
> that correct ?

 That's right - rather than pre-populating a representation of the
 entire OpenFlow state, the ofproto-dpif implementation uses an
 "upcall" model where the datapath acts as a cache for forwarding
 behaviour, and the cache is populated on-demand as traffic arrives.
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Re: [ovs-discuss] OVS megaflows

[Joe Stringer]

The FAQ is referring to megaflows as well, the reasons are the same.
Neither microflows nor megaflows can be pre-populated.

On 14 August 2017 at 00:35, Sara Gittlin  wrote:
> I  understand that this citation refers to the kernel microflows  tables.
> the kernel megaflows table *can be* pre-populated. Correct ?
> Sara
>
> On Mon, Aug 14, 2017 at 9:31 AM, Sara Gittlin  wrote:
>> Thanks you Joe
>> the following citation is in a contradiction to the idea of
>> pre-populating megaflows in kernel datapath .
>> this is from  http://docs.openvswitch.org/en/latest/faq/design/
>>
>> "Q: Can OVS populate the kernel flow table in advance instead of in
>> reaction to packets?
>>
>> A: No. There are several reasons:
>>
>> Kernel flows are not as sophisticated as OpenFlow flows, which means
>> that some OpenFlow policies could require a large number of kernel
>> flows. The “conjunctive match” feature is an extreme example: the
>> number of kernel flows it requires is the product of the number of
>> flows in each dimension.
>> With multiple OpenFlow flow tables and simple sets of actions, the
>> number of kernel flows required can be as large as the product of the
>> number of flows in each dimension. With more sophisticated actions,
>> the number of kernel flows could be even larger.
>> Open vSwitch is designed so that any version of OVS userspace
>> interoperates with any version of the OVS kernel module. This forward
>> and backward compatibility requires that userspace observe how the
>> kernel module parses received packets. This is only possible in a
>> straightforward way when userspace adds kernel flows in reaction to
>> received packets."
>>
>> Thanks in advance - Sara
>>
>> On Mon, Jul 24, 2017 at 10:58 PM, Joe Stringer  wrote:
>>> On 23 July 2017 at 06:37, Sara Gittlin  wrote:
 Hello,
 I understand that there is a support for megaflows in the kernel and 
 netlink.
 I also understand that there is no megaflow implementation in ofproto.
 i.e. there is no implementation of compressing (if possible) all flows
 in ofproto table to megaflows and installing it in the datapath. is
 that correct ?
>>>
>>> That's right - rather than pre-populating a representation of the
>>> entire OpenFlow state, the ofproto-dpif implementation uses an
>>> "upcall" model where the datapath acts as a cache for forwarding
>>> behaviour, and the cache is populated on-demand as traffic arrives.
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Re: [ovs-discuss] OVS megaflows

[Sara Gittlin]

I  understand that this citation refers to the kernel microflows  tables.
the kernel megaflows table *can be* pre-populated. Correct ?
Sara

On Mon, Aug 14, 2017 at 9:31 AM, Sara Gittlin  wrote:
> Thanks you Joe
> the following citation is in a contradiction to the idea of
> pre-populating megaflows in kernel datapath .
> this is from  http://docs.openvswitch.org/en/latest/faq/design/
>
> "Q: Can OVS populate the kernel flow table in advance instead of in
> reaction to packets?
>
> A: No. There are several reasons:
>
> Kernel flows are not as sophisticated as OpenFlow flows, which means
> that some OpenFlow policies could require a large number of kernel
> flows. The “conjunctive match” feature is an extreme example: the
> number of kernel flows it requires is the product of the number of
> flows in each dimension.
> With multiple OpenFlow flow tables and simple sets of actions, the
> number of kernel flows required can be as large as the product of the
> number of flows in each dimension. With more sophisticated actions,
> the number of kernel flows could be even larger.
> Open vSwitch is designed so that any version of OVS userspace
> interoperates with any version of the OVS kernel module. This forward
> and backward compatibility requires that userspace observe how the
> kernel module parses received packets. This is only possible in a
> straightforward way when userspace adds kernel flows in reaction to
> received packets."
>
> Thanks in advance - Sara
>
> On Mon, Jul 24, 2017 at 10:58 PM, Joe Stringer  wrote:
>> On 23 July 2017 at 06:37, Sara Gittlin  wrote:
>>> Hello,
>>> I understand that there is a support for megaflows in the kernel and 
>>> netlink.
>>> I also understand that there is no megaflow implementation in ofproto.
>>> i.e. there is no implementation of compressing (if possible) all flows
>>> in ofproto table to megaflows and installing it in the datapath. is
>>> that correct ?
>>
>> That's right - rather than pre-populating a representation of the
>> entire OpenFlow state, the ofproto-dpif implementation uses an
>> "upcall" model where the datapath acts as a cache for forwarding
>> behaviour, and the cache is populated on-demand as traffic arrives.
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