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Date: Tue, 26 Jul 2022 20:49:45 +0000 From: Parav Pandit <parav@...dia.com> To: "Michael S. Tsirkin" <mst@...hat.com> CC: "Zhu, Lingshan" <lingshan.zhu@...el.com>, "jasowang@...hat.com" <jasowang@...hat.com>, "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 > From: Michael S. Tsirkin <mst@...hat.com> > Sent: Tuesday, July 26, 2022 3:52 PM > > On Tue, Jul 26, 2022 at 03:56:32PM +0000, 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. > > 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. > > Yes that's fine. And if we just didn't return anything without MQ that would be > fine. But IIUC netlink reports the # of pairs regardless, it just puts 0 there. I read it differently at [1] which checks for the MQ feature bit. [1] https://elixir.bootlin.com/linux/latest/source/drivers/vdpa/vdpa.c#L825 > > -- > MST
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