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

[Shahaf Shuler <shahafs@mellanox.com>]

Tuesday, April 24, 2018 1:39 PM, Ferruh Yigit:
> Subject: Re: [dpdk-dev] Survey for final decision about per-port offload API
> 
> 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:
> >
> >
> https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdpd
> k
> > .org%2Fml%2Farchives%2Fdev%2F2018-
> March%2F094023.html&data=02%7C01%7Cs
> >
> hahafs%40mellanox.com%7C3d6dec1702a344bbfa0708d5a9cfacad%7Ca65297
> 1c7d2
> >
> e4d9ba6a4d149256f461b%7C0%7C0%7C636601631811623875&sdata=LVYRf4B
> i1lh9E
> > u8M9zwgBxdlKI7V0YYsx2%2FvfCim2tU%3D&reserved=0
> >
> > It was also proposed to relax the API and allow "forgetting" port
> > offloads in queue offloads:
> >
> >
> https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdpd
> k
> > .org%2Fml%2Farchives%2Fdev%2F2018-
> March%2F092978.html&data=02%7C01%7Cs
> >
> hahafs%40mellanox.com%7C3d6dec1702a344bbfa0708d5a9cfacad%7Ca65297
> 1c7d2
> >
> e4d9ba6a4d149256f461b%7C0%7C0%7C636601631811623875&sdata=8V4DdP
> uIIGpxW
> > 8i7AtaB1aB536JC6X6cqdSwaQOMRIo%3D&reserved=0
> >
> > 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.
> 
> 

In other words - queue configuration can effect queue offloads and port configuration can effect port offloads.

I am OK with that. 


> 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]