netdev - Re: [PATCH V3 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F

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Message-ID: <19681358-fc81-be5b-c20b-7394a549f0be@intel.com>
Date:   Wed, 27 Jul 2022 10:14:53 +0800
From:   "Zhu, Lingshan" <lingshan.zhu@...el.com>
To:     Parav Pandit <parav@...dia.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "mst@...hat.com" <mst@...hat.com>
Cc:     "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "xieyongji@...edance.com" <xieyongji@...edance.com>,
        "gautam.dawar@....com" <gautam.dawar@....com>
Subject: Re: [PATCH V3 5/6] vDPA: answer num of queue pairs = 1 to userspace
 when VIRTIO_NET_F_MQ == 0



On 7/26/2022 11:56 PM, Parav Pandit wrote:
>> From: Zhu, Lingshan <lingshan.zhu@...el.com>
>> Sent: Tuesday, July 12, 2022 11:46 PM
>>> When the user space which invokes netlink commands, detects that _MQ
>> is not supported, hence it takes max_queue_pair = 1 by itself.
>> I think the kernel module have all necessary information and it is the only
>> one which have precise information of a device, so it should answer precisely
>> than let the user space guess. The kernel module should be reliable than stay
>> silent, leave the question to the user space tool.
> Kernel is reliable. It doesn’t expose a config space field if the field doesn’t exist regardless of field should have default or no default.
so when you know it is one queue pair, you should answer one, not try to 
guess.
> User space should not guess either. User space gets to see if _MQ present/not present. If _MQ present than get reliable data from kernel.
> If _MQ not present, it means this device has one VQ pair.
it is still a guess, right? And all user space tools implemented this 
feature need to guess