[dpdk-dev] Survey for final decision about per-port offload API

[Ferruh Yigit]

On 3/30/2018 2:47 PM, Thomas Monjalon wrote:
> There are some discussions about a specific part of the offload API:
> 	"To enable per-port offload, the offload should be set on both
> 	device configuration and queue setup."
> 
> It means the application must repeat the port offload flags
> in rte_eth_conf.[rt]xmode.offloads and rte_eth_[rt]xconf.offloads,
> when calling respectively rte_eth_dev_configure() and
> rte_eth_[rt]x_queue_setup for each queue.
> 
> The PMD must check if there is mismatch, i.e. a port offload not
> repeated in queue setup.
> There is a proposal to do this check at ethdev level:
> 	http://dpdk.org/ml/archives/dev/2018-March/094023.html
> 
> It was also proposed to relax the API and allow "forgetting" port
> offloads in queue offloads:
> 	http://dpdk.org/ml/archives/dev/2018-March/092978.html
> 
> It would mean the offloads applied to a queue result of OR operation:
> 	rte_eth_conf.[rt]xmode.offloads | rte_eth_[rt]xconf.offloads
> 
> 1/ Do you agree with above API change?

There is a detail of ability to disabling queue level offloads in queue_setup()
function, I want to discuss here.

Prolog:
port level offload: An offload only can be applied port level, to all queues.
queue level offload: An offload can be applied into individual queues of the port

PMD reports port offload capability: port level offload + queue level offload
PMD reports queue offload capability: queue level offload


Above suggested change to API:
- Application will be limited in configure() to set only an offload within "port
offload capability"
- Application will be limited in queue_setup() to set only an offload within
"queue offload capability"


This doesn't say much about disabling an offload in queue_setup(), as a rule:
- An "port level offload" can't be disabled in queue_setup()


There are two cases of disable:
1- Disabling a "queue level offload" enabled queue_setup() previously
2- Disabling a "queue level offload" enabled in configure()

If second is not supported, to disable the offload, applications should
stop->re-configure()->re-queue_setup()->start the port. But having this
capability makes the offloading parameters more confusing for applications.


I suggest adding disable support to fist one but not second one.

According this,
application:
- In configure() set offload within "port offload capability"
- In queue_setup() set offload within "queue offload capability". Offloads are
incremental to ones in configure()

PMDs:
- In configure() verify the offload against "port offload capability"
- In queue_setup() verify the offload against "queue offload capability"
- In queue_setup() if requested offload is not enabled already, enable it for queue
- In queue_setup() if an offload value cleared in requested offload that is set
in port_offload, return error.
- In queue_setup() if an offload value cleared in requested offload that is not
set in port_offload but set in queue_offload, disable it for that queue.


Samples according initial suggestion + disable support:

Sample 1:
port level offload: A, B
queue level offload: C, D
port offload capability: A, B, C, D
queue offload capability: C, D

configure(A,C): Q1:A,C  Q2:A,C [queue_setup() can't disable A,C after this]
queue_setup(Q1, B): --> Error [Can't enable port level offload in queue_setup()]
queue_setup(Q1, D): Q1:A,C,D
queue_setup(Q1, ""): Q1:A,C [Disabled D]
queue_setup(Q2, "C,D"): Q2:A,C,D
queue_setup(Q2, ""): Q2:A,C
queue_setup(Q2, A): --> Error [A is port_level offload]


Sample 2:
port level offload: A, B, C
queue level offload: ""
port offload capability: A, B, C
queue offload capability: ""   [no way to change offloads in queue level]

configure(A,C): Q1:A,C  Q2:A,C
queue_setup(Q1, B): --> Error
queue_setup(Q1, A): --> Error
queue_setup(Q2, ""): Q2:A,C
queue_setup(Q1, ""): Q1:A,C


Sample 3:
port level offload: ""
queue level offload: A, B, C, D
port offload capability: A, B, C, D
queue offload capability: A, B, C, D

configure(A): Q1:A  Q2:A
queue_setup(Q1, A): Q1:A
queue_setup(Q1, ""): Q1:A
queue_setup(Q1, A,B,C,D): Q1:A,B,C,D
queue_setup(Q1, B): Q1:A,B [Disable C,D]
queue_setup(Q2, C): Q2:A,C
queue_setup(Q1, ""): Q1:A [Disable B]
queue_setup(Q2, ""): Q2:A [Disable C]