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Thu, 23 Dec 2021 02:43:42 +0000 Message-ID: <47ce323e-c2e4-cf13-063e-78067c03a4d4@oracle.com> Date: Wed, 22 Dec 2021 18:43:38 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH v5 10/13] vdpa: Support reporting max device virtqueues Content-Language: en-US To: Jason Wang References: <20211221172006.43784-1-elic@nvidia.com> <20211221172006.43784-11-elic@nvidia.com> <20211222064728.GE210450@mtl-vdi-166.wap.labs.mlnx> <20211222071036.GA213382@mtl-vdi-166.wap.labs.mlnx> <84292943-b4de-8162-1fde-fcfab479b629@oracle.com> <20211222075402.GA214545@mtl-vdi-166.wap.labs.mlnx> <8e93cfc4-b71e-adc5-8b35-337523e3a431@oracle.com> From: Si-Wei Liu Organization: Oracle Corporation In-Reply-To: X-ClientProxiedBy: BY5PR17CA0057.namprd17.prod.outlook.com (2603:10b6:a03:167::34) To BYAPR10MB3287.namprd10.prod.outlook.com (2603:10b6:a03:15c::11) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: b4d189fe-e97d-4cfc-1285-08d9c5be086a X-MS-TrafficTypeDiagnostic: BY5PR10MB3796:EE_ X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; 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charset="us-ascii"; Format="flowed" Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On 12/22/2021 6:27 PM, Jason Wang wrote: > On Thu, Dec 23, 2021 at 3:25 AM Si-Wei Liu wrote: >> >> >> On 12/21/2021 11:54 PM, Eli Cohen wrote: >>> On Tue, Dec 21, 2021 at 11:29:36PM -0800, Si-Wei Liu wrote: >>>> On 12/21/2021 11:10 PM, Eli Cohen wrote: >>>>> On Wed, Dec 22, 2021 at 09:03:37AM +0200, Parav Pandit wrote: >>>>>>> From: Eli Cohen >>>>>>> Sent: Wednesday, December 22, 2021 12:17 PM >>>>>>> >>>>>>>>>> --- a/drivers/vdpa/vdpa.c >>>>>>>>>> +++ b/drivers/vdpa/vdpa.c >>>>>>>>>> @@ -507,6 +507,9 @@ static int vdpa_mgmtdev_fill(const struct >>>>>>>>> vdpa_mgmt_dev *mdev, struct sk_buff *m >>>>>>>>>> err = -EMSGSIZE; >>>>>>>>>> goto msg_err; >>>>>>>>>> } >>>>>>>>>> + if (nla_put_u16(msg, VDPA_ATTR_DEV_MGMTDEV_MAX_VQS, >>>>>>>>>> + mdev->max_supported_vqs)) >>>>>>>>> It still needs a default value when the field is not explicitly >>>>>>>>> filled in by the driver. >>>>>>>>> >>>>>>>> Unlikely. This can be optional field to help user decide device max limit. >>>>>>>> When max_supported_vqs is set to zero. Vdpa should omit exposing it to user >>>>>>> space. >>>>>>> This is not about what you expose to userspace. It's about the number of VQs >>>>>>> you want to create for a specific instance of vdpa. >>>>>> This value on mgmtdev indicates that a given mgmt device supports creating a vdpa device who can have maximum VQs of N. >>>>>> User will choose to create VQ with VQs <= N depending on its vcpu and other factors. >>>>> You're right. >>>>> So each vendor needs to put there their value. >>>> If I understand Parav correctly, he was suggesting not to expose >>>> VDPA_ATTR_DEV_MGMTDEV_MAX_VQS to userspace if seeing (max_supported_vqs == >>>> 0) from the driver. >>> I can see the reasoning, but maybe we should leave it as zero which >>> means it was not reported. The user will then need to guess. I believe >>> other vendors will follow with an update so this to a real value. >> Unless you place a check in the vdpa core to enforce it on vdpa >> creation, otherwise it's very likely to get ignored by other vendors. >> >>>> But meanwhile, I do wonder how users tell apart multiqueue supporting parent >>>> from the single queue mgmtdev without getting the aid from this field. I >>>> hope the answer won't be to create a vdpa instance to try. >>>> >>> Do you see a scenario that an admin decides to not instantiate vdpa just >>> because it does not support MQ? >> Yes, there is. If the hardware doesn't support MQ, the provisioning tool >> in the mgmt software will need to fallback to software vhost backend >> with mq=on. At the time the tool is checking out, it doesn't run with >> root privilege. >> >>> And it the management device reports it does support, there's still no >>> guarantee you'll end up with a MQ net device. >> I'm not sure I follow. Do you mean it may be up to the guest feature >> negotiation? But the device itself is still MQ capable, isn't it? > I think we need to clarify the "device" here. > > For compatibility reasons, there could be a case that mgmt doesn't > expect a mq capable vdpa device. So in this case, even if the parent > is MQ capable, the vdpa isn't. Right. The mgmt software is not necessarily libvirt. Perhaps I should be explicit to say the mgmt software we're building would definitely create MQ vdpa device in case on a MQ capable parent. -Siwei > > Thanks > >> Thanks, >> -Siwei >> >>> >>>> -Siwei >>>> >>>>>> This is what is exposed to the user to decide the upper bound. >>>>>>>> There has been some talk/patches of rdma virtio device. >>>>>>>> I anticipate such device to support more than 64K queues by nature of rdma. >>>>>>>> It is better to keep max_supported_vqs as u32. >>>>>>> Why not add it when we have it? >>>>>> Sure, with that approach we will end up adding two fields (current u16 and later another u32) due to smaller bit width of current one. >>>>>> Either way is fine. Michael was suggesting similar higher bit-width in other patches, so bringing up here for this field on how he sees it. >>>>> I can use u32 then. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization