Re: [dpdk-dev] [PATCH 3/9] vdpa/ifc: add support to vDPA queue enable

["Wang, Xiao W" <xiao.w.wang@intel.com>]

Hi,

Comments inline.

Best Regards,
Xiao

> -----Original Message-----
> From: Jason Wang <jasowang@redhat.com>
> Sent: Friday, May 15, 2020 6:09 PM
> To: Wang, Xiao W <xiao.w.wang@intel.com>; Maxime Coquelin
> <maxime.coquelin@redhat.com>; Ye, Xiaolong <xiaolong.ye@intel.com>;
> shahafs@mellanox.com; matan@mellanox.com; amorenoz@redhat.com;
> viacheslavo@mellanox.com; dev@dpdk.org
> Cc: lulu@redhat.com; Xu, Rosen <rosen.xu@intel.com>
> Subject: Re: [PATCH 3/9] vdpa/ifc: add support to vDPA queue enable
> 
> 
> On 2020/5/15 下午5:42, Wang, Xiao W wrote:
> >
> > Hi,
> >
> > Best Regards,
> >
> > Xiao
> >
> > > -----Original Message-----
> >
> > > From: Jason Wang <jasowang@redhat.com>
> >
> > > Sent: Friday, May 15, 2020 5:09 PM
> >
> > > To: Maxime Coquelin <maxime.coquelin@redhat.com>; Ye, Xiaolong
> >
> > > <xiaolong.ye@intel.com>; shahafs@mellanox.com; matan@mellanox.com;
> >
> > > amorenoz@redhat.com; Wang, Xiao W <xiao.w.wang@intel.com>;
> >
> > > viacheslavo@mellanox.com; dev@dpdk.org
> >
> > > Cc: lulu@redhat.com
> >
> > > Subject: Re: [PATCH 3/9] vdpa/ifc: add support to vDPA queue enable
> >
> > >
> >
> > >
> >
> > > On 2020/5/14 下午4:02, Maxime Coquelin wrote:
> >
> > > > This patch adds support to enabling and disabling
> >
> > > > vrings on a per-vring granularity.
> >
> > > >
> >
> > > > Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com
> > <mailto:maxime.coquelin@redhat.com>>
> >
> > >
> >
> > >
> >
> > > A question here, I see in qemu peer_attach() may try to generate
> >
> > > VHOST_USER_SET_VRING_ENABLE, but just from the name I think it should
> >
> > > behave as queue_enable defined in virtio specification which is
> >
> > > explicitly under the control of guest?
> >
> > >
> >
> > > (Note, in Cindy's vDPA series, we must invent new vhost_ops to differ
> >
> > > from this one).
> >
> > From my view, common_cfg.enable reg is used for registering a queue to
> > hypervisor&vhost, but not ENABLE.
> >
> 
> Well, what's your definition of "enable" in this context?

"Enable a queue" means traffic can pass through this queue.

> 
> Spec said:
> 
> queue_enable
>     The driver uses this to selectively prevent the device from
>     executing requests from this virtqueue. 1 - enabled; 0 - disabled.
> 
> This means, if queue_enable is not set to 1, device can not execute
> request for this specific virtqueue.
> 

For queue enabling in virtio MQ case, there're 2 steps needed:
1. select a queue and write 1 to common_cfg.enable reg
2. send control vq message VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET
If no step2, by default there's only 1 queue pair enabled.

> 
> > The control queue message VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET is for
> > enable/disable queue pairs.
> >
> 
> But in qemu this is hooked to VHOST_USER_SET_VRING_ENABLE, see
> peer_attach(). And this patch hook VHOST_USER_SET_VRING_ENABLE to
> queue_enable.
> 
> This means IFCVF uses queue_enable instead of control vq or other
> register for setting multiqueue stuff? My understanding is that IFCVF
> has dedicated register to do this.
> 
> Note setting mq is different from queue_enable, changing the number of
> queues should let the underlayer NIC to properly configure its
> steering/switching/filtering logic to make sure traffic were only sent
> to the queues that is set by driver.
> 
> So hooking VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET to queue_enable looks
> wrong.

We are on the same page. As I said we have dedicated reg designed to enable MQ (ensure traffic only sent to queues enabled by user) in VDPA case.

> 
> 
> > Think about when virtio net probes, all queues are selected and
> > "enabled" by init_vqs(),
> >
> 
> I think we're talking about aligning the implementation with spec not
> just make it work for some specific drivers. Driver may choose to not
> enable a virtqueue by not setting 1 to queue_enable.
> 
> Thanks
> 
> 
> > but MQ is not enabled until virtnet_set_channels() by user config with
> > "ethtool".
> >
> > Based on this, below reg writing is not OK to enable MQ. IFC HW
> > supports below registers for VF pass-thru case.
> >
> > Actually, we have specific reg designed to enable MQ in VDPA case.
> >
> > > > +IFCVF_WRITE_REG16(qid, &cfg->queue_select);
> >
> > > > +IFCVF_WRITE_REG16(enable, &cfg->queue_enable);
> >
> > BRs,
> >
> > Xiao
> >
> > >
> >
> > > Thanks
> >
> > >
> >
> > >
> >
> > > > ---
> >
> > > >drivers/vdpa/ifc/base/ifcvf.c |9 +++++++++
> >
> > > >drivers/vdpa/ifc/base/ifcvf.h |4 ++++
> >
> > > >drivers/vdpa/ifc/ifcvf_vdpa.c | 23 ++++++++++++++++++++++-
> >
> > > >3 files changed, 35 insertions(+), 1 deletion(-)
> >
> > > >
> >
> > > > diff --git a/drivers/vdpa/ifc/base/ifcvf.c
> > b/drivers/vdpa/ifc/base/ifcvf.c
> >
> > > > index 3c0b2dff66..dd4e7468ae 100644
> >
> > > > --- a/drivers/vdpa/ifc/base/ifcvf.c
> >
> > > > +++ b/drivers/vdpa/ifc/base/ifcvf.c
> >
> > > > @@ -327,3 +327,12 @@ ifcvf_get_queue_notify_off(struct ifcvf_hw
> > *hw, int
> >
> > > qid)
> >
> > > >return (u8 *)hw->notify_addr[qid] -
> >
> > > >(u8 *)hw->mem_resource[hw->notify_region].addr;
> >
> > > >}
> >
> > > > +
> >
> > > > +void
> >
> > > > +ifcvf_queue_enable(struct ifcvf_hw *hw, u16 qid,u16 enable)
> >
> > > > +{
> >
> > > > +struct ifcvf_pci_common_cfg *cfg = hw->common_cfg;
> >
> > > > +
> >
> > > > +IFCVF_WRITE_REG16(qid, &cfg->queue_select);
> >
> > > > +IFCVF_WRITE_REG16(enable, &cfg->queue_enable);
> >
> > > > +}
> >
> > > > diff --git a/drivers/vdpa/ifc/base/ifcvf.h
> > b/drivers/vdpa/ifc/base/ifcvf.h