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From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: Shahaf Shuler <shahafs@mellanox.com>,
	"tiwei.bie@intel.com" <tiwei.bie@intel.com>,
	"zhihong.wang@intel.com" <zhihong.wang@intel.com>,
	"amorenoz@redhat.com" <amorenoz@redhat.com>,
	"xiao.w.wang@intel.com" <xiao.w.wang@intel.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"jfreimann@redhat.com" <jfreimann@redhat.com>
Cc: "stable@dpdk.org" <stable@dpdk.org>, Matan Azrad <matan@mellanox.com>
Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH 00/15] Introduce Virtio vDPA driver
Date: Wed, 11 Sep 2019 09:15:20 +0200
Message-ID: <b9486796-8f94-190f-7df8-073af1475b6f@redhat.com> (raw)
In-Reply-To: <AM0PR0502MB379542B09EC7252A2BEC096DC3B10@AM0PR0502MB3795.eurprd05.prod.outlook.com>



On 9/11/19 7:15 AM, Shahaf Shuler wrote:
> Tuesday, September 10, 2019 4:56 PM, Maxime Coquelin:
>> Subject: Re: [dpdk-dev] [PATCH 00/15] Introduce Virtio vDPA driver
>> On 9/10/19 3:44 PM, Shahaf Shuler wrote:
>>> Tuesday, September 10, 2019 10:46 AM, Maxime Coquelin:
>>>> Subject: Re: [dpdk-dev] [PATCH 00/15] Introduce Virtio vDPA driver
> 
> [...]
> 
>>>>
>>>> Hi Shahaf,
>>>>
>>>>
>>>> IMHO, I see two uses cases where it can make sense to use vDPA with a
>>>> full offload HW device:
>>>> 1. Live-migration support:  It makes it possible to switch to rings
>>>>    processing in SW during the migration as Virtio HH does not support
>>>>    dirty pages logging.
>>>
>>> Can you elaborate why specifically using virtio_vdpa PMD enables this SW
>> relay during migration?
>>> e.g. the vdpa PMD of intel that runs on top of VF do that today as well.
>>
>> I think there were a misunderstanding. When I said:
>> "
>> I see two uses cases where it can make sense to use vDPA with a full offload
>> HW device "
>>
>> I meant, I see two uses cases where it can make sense to use vDPA with a full
>> offload HW device, instead of the full offload HW device to use Virtio PMD.
>>
>> In other words, I think it is preferable to only offload the datapath, so that it
>> is possible to support SW live-migration.
>>
>>>>
>>>> 2. Can be used to provide a single standard interface (the vhost-user
>>>>    socket) to containers in the scope of CNFs. Doing so, the container
>>>>    does not need to be modified, whatever the HW NIC: Virtio datapath
>>>>    offload only, full Virtio offload, or no offload at all. In the
>>>>    latter case, it would not be optimal as it implies forwarding between
>>>>    the Vhost PMD and the HW NIC PMD but it would work.
>>>
>>> It is not clear to me the interface map in such system.
>>> From what I understand the container will have virtio-user i/f and the host
>> will have virtio i/f. then the virtio i/f can be programmed to work w/ vDPA or
>> not.
>>> For full emulation I guess you will need to expose the netdev of the fully
>> emulated virtio device to the container?
>>>
>>> Am trying to map when it is beneficial to use this virtio_vdpa PMD and
>> when it is better to use the vendor specific vDPA PMD on top of VF.
>>
>> I think that with above clarification, I made it clear that the goal of this driver
>> is not to replace vendors vDPA drivers (their control path maybe not even be
>> compatible), but instead to provide a generic driver that can be used either
>> within a guest with a para-virtualized Virtio- net device or with HW NIC that
>> fully offloads Virtio (both data and control paths).
> 
> Thanks Maxim, It is clearer now. 
> From what I understand this driver is to be used w/ vDPA when the underlying device is virtio. 
> 
> I can perfectly understand the para-virt ( + nested virtualization / container inside VM) use case. 
> 
> Regarding the fully emulated virtio device on the host (instead of a plain VF) - for me the benefit still not clear - if you have HW that can expose VF why not use VF + vendor specific vDPA driver.

If you need a vendor specific vDPA driver for the VF, then you
definitely want to use the vendor specific driver.

However, if there is a HW or VF that implements the Virtio Spec even for
the control path (i.e. the PCI registers layout), one may be tempted to
do device assignment directly to the guest and use Virtio PMD.
The downside of doing that is it won't support live-migration.

The benefit of using vDPA with virtio vDPA driver in this case is
provide a way to support live-migration (by switch to SW ring processing
and perform dirty pages logging).

> 
> Anyway - for the series,
> Acked-by: Shahaf Shuler <shahafs@mellanox.com>
> 

Thanks!
Maxime

  reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-29  7:59 [dpdk-stable] " Maxime Coquelin
2019-08-29  7:59 ` [dpdk-stable] [PATCH 01/15] vhost: remove vhost kernel header inclusion Maxime Coquelin
2019-09-02  6:03   ` Tiwei Bie
2019-09-03  7:24     ` Maxime Coquelin
2019-08-29  7:59 ` [dpdk-stable] [PATCH 02/15] vhost: configure vDPA as soon as the device is ready Maxime Coquelin
2019-09-02  8:34   ` Ye Xiaolong
2019-09-02  9:02     ` Wang, Xiao W
2019-09-03  7:34       ` Maxime Coquelin
2019-09-03 10:58         ` Wang, Xiao W
2019-08-29  7:59 ` [dpdk-stable] [PATCH 03/15] net/virtio: move control path fonctions in virtqueue file Maxime Coquelin
2019-09-02  6:05   ` Tiwei Bie
2019-08-29  7:59 ` [dpdk-stable] [PATCH 04/15] net/virtio: add virtio PCI subsystem device ID declaration Maxime Coquelin
2019-09-02  6:14   ` Tiwei Bie
2019-09-03  7:25     ` Maxime Coquelin
2019-08-29  7:59 ` [dpdk-stable] [PATCH 05/15] net/virtio: save notify bar ID in virtio HW struct Maxime Coquelin
2019-09-02  6:17   ` Tiwei Bie
2019-08-29  7:59 ` [dpdk-stable] [PATCH 06/15] net/virtio: add skeleton for virtio vDPA driver Maxime Coquelin
2019-09-02  6:27   ` Tiwei Bie
2019-09-03  7:25     ` Maxime Coquelin
2019-08-29  7:59 ` [dpdk-stable] [PATCH 07/15] net/virtio: add vDPA ops to get number of queue Maxime Coquelin
2019-09-02  6:32   ` Tiwei Bie
2019-08-29  7:59 ` [dpdk-stable] [PATCH 08/15] net/virtio: add virtio vDPA op to get features Maxime Coquelin
2019-09-02  6:43   ` Tiwei Bie
2019-09-03  7:27     ` Maxime Coquelin
2019-08-29  7:59 ` [dpdk-stable] [PATCH 09/15] net/virtio: add virtio vDPA op to get protocol features Maxime Coquelin
2019-09-02  6:46   ` Tiwei Bie
2019-08-29  7:59 ` [dpdk-stable] [PATCH 10/15] net/virtio: add vDPA op to configure and start the device Maxime Coquelin
2019-09-03  5:30   ` Tiwei Bie
2019-09-03  7:40     ` Maxime Coquelin
2019-09-03  8:49       ` Tiwei Bie
2019-09-04  4:06         ` Jason Wang
2019-09-04  6:56           ` Maxime Coquelin
2019-09-05  2:57             ` Tiwei Bie
2019-08-29  7:59 ` [dpdk-stable] [PATCH 11/15] net/virtio: add vDPA op to stop and close " Maxime Coquelin
2019-09-02  7:07   ` Tiwei Bie
2019-09-03  7:30     ` Maxime Coquelin
2019-08-29  7:59 ` [dpdk-stable] [PATCH 12/15] net/virtio: add vDPA op to set features Maxime Coquelin
2019-08-29  7:59 ` [dpdk-stable] [PATCH 13/15] net/virtio: add vDPA ops to get VFIO FDs Maxime Coquelin
2019-09-03  4:47   ` Tiwei Bie
2019-08-29  7:59 ` [dpdk-stable] [PATCH 14/15] net/virtio: add vDPA op to get notification area Maxime Coquelin
2019-09-03  5:02   ` Tiwei Bie
2019-09-03  7:36     ` Maxime Coquelin
2019-09-03  8:40       ` Tiwei Bie
2019-08-29  8:00 ` [dpdk-stable] [PATCH 15/15] doc: add documentation for Virtio vDPA driver Maxime Coquelin
2019-09-09 11:55 ` [dpdk-stable] [dpdk-dev] [PATCH 00/15] Introduce " Shahaf Shuler
2019-09-10  7:46   ` Maxime Coquelin
2019-09-10 13:44     ` Shahaf Shuler
2019-09-10 13:56       ` Maxime Coquelin
2019-09-11  5:15         ` Shahaf Shuler
2019-09-11  7:15           ` Maxime Coquelin [this message]
2019-10-24  6:32 ` [dpdk-stable] " Maxime Coquelin

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