Re: [dpdk-dev] [PATCH] net/vdev_netvsc: print warning if Mellanox devices are not configured

[Thomas Monjalon <thomas@monjalon.net>]

24/05/2019 18:48, Stephen Hemminger:
> On Fri, 24 May 2019 18:38:53 +0200
> Thomas Monjalon <thomas@monjalon.net> wrote:
> > 24/05/2019 18:07, Stephen Hemminger:
> > > On Fri, 24 May 2019 14:26:40 +0100
> > > Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> > >   
> > > > On 5/23/2019 11:01 PM, Stephen Hemminger wrote:  
> > > > > Several users have run into problems where the MLX drivers were not
> > > > > enabled in their build. And then trying to run their DPDK
> > > > > application on Azure. What happens is that all packets
> > > > > go over the slow path, and failsafe repeatedly probes for never
> > > > > existing sub-device.
> > > > > 
> > > > > Both Mellanox drivers should be checked. MLX4 for current versions,
> > > > > and MLX5 for future upgrades. This code is only called if Hyper-V/Azure
> > > > > is detected.
> > > > > 
> > > > > Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
> > > > > ---
> > > > >  drivers/net/vdev_netvsc/vdev_netvsc.c | 7 +++++++
> > > > >  1 file changed, 7 insertions(+)
> > > > > 
> > > > > diff --git a/drivers/net/vdev_netvsc/vdev_netvsc.c b/drivers/net/vdev_netvsc/vdev_netvsc.c
> > > > > index 801f54c96e01..64f9dbf66e18 100644
> > > > > --- a/drivers/net/vdev_netvsc/vdev_netvsc.c
> > > > > +++ b/drivers/net/vdev_netvsc/vdev_netvsc.c
> > > > > @@ -812,6 +812,13 @@ vdev_netvsc_scan_callback(__rte_unused void *arg)
> > > > >  	struct rte_devargs *devargs;
> > > > >  	struct rte_bus *vbus = rte_bus_find_by_name("vdev");
> > > > >  
> > > > > +#ifndef RTE_LIBRTE_MLX4_PMD
> > > > > +	DRV_LOG(WARNING, "Mellanox MLX4 not configured.");
> > > > > +#endif
> > > > > +#ifndef RTE_LIBRTE_MLX5_PMD
> > > > > +	DRV_LOG(WARNING, "Mellanox MLX5 not configured.");
> > > > > +#endif    
> > > > 
> > > > Is it OK a virtual PMD being this much aware of another PMD?
> > > > Can it be an option to add this check into build system? And if there is direct
> > > > dependency perhaps even don't compile the 'vdev_netvsc' when none mlx PMD is
> > > > enabled.  
> > > 
> > > vdev_netvsc is not a device, it is really just a hack to start other
> > > device drivers on Hyper-V/Azure.  If the build system supported dependencies
> > > (like Linux kbuild) this would not be necessary. Meson only does dynamic dependencies
> > > so that doesn't help.
> > > 
> > > This is a warning and not fatal only because application will still at
> > > least run, and somebody may want to run with SR-IOV with Intel NIC's on Hyper-V.
> > > 
> > > 
> > > The warning is just to give users better immediate feedback rather than
> > > trying to diagnose poor performance or mystery device not found messages.  
> > 
> > 
> > It really looks strange to me.
> > What you need is to fail at compilation if requested PMD is not built.
> > I would advise to work on a script to configure meson.
> 
> None of the people that ran into this were using meson build.
> For example, VPP doesn't use meson.

They will use meson when makefile will be removed :)

Anyway, no matter the build system, what we want is a way
to guide users to a proper DPDK installation.
Your solution is to add some very specific logs.
My proposal is to guide the user with a script and some
specific parameters so it will fail if a required dependency is not met.