Re: [dpdk-dev] [PATCH] bus/pci: optimize pci device probe

[Thomas Monjalon <thomas@monjalon.net>]

26/04/2020 20:41, Jerin Jacob:
> On Sun, Apr 26, 2020 at 11:38 PM Thomas Monjalon <thomas@monjalon.net> wrote:
> >
> > 26/04/2020 19:38, jerinj@marvell.com:
> > > From: Jerin Jacob <jerinj@marvell.com>
> > >
> > > If the PCI device is not attached to any driver then there is no
> > > point in probing it. As an optimization, skip the PCI device probe if
> > > the PCI device driver of type RTE_KDRV_NONE.
> > >
> > > Signed-off-by: Jerin Jacob <jerinj@marvell.com>
> > > ---
> > > Notes:
> > > ------
> > > - virtio drivers does special treatment based on RTE_KDRV_UNKNOWN, That is
> > > the reason allowing RTE_KDRV_UNKNOWN in this patch.
> > > - virio devices uses RTE_KDRV_UNKNOWN for some special meaning, IMO, if it would
> > >   be better, if
> > > a) Introduce the KDRV for virio
> > > b) If the PCIe device of driver type NONE or UNKNOWN then not even add in pci
> > > list
> > > in the scan, It will improve the boot time by avoiding operation on
> > > unwanted device like sorting the PCI devices, scanning it, probe it, managing
> > > it etc.
> >
> > mlx4/mlx4 uses RTE_KDRV_UNKNOWN.
> 
> OK.
> 
> > > - Initial problem reported at http://patches.dpdk.org/patch/64999/ as
> > > boot time printf clutter on octeontx2 devices with a lot PCI devices which are
> > > of type RTE_KDRV_NONE.
> >
> > Add a logtype for PCI driver and adjust log level accordingly
> > to your preferences.
> >
> > > @@ -271,6 +271,8 @@ pci_probe_all_drivers(struct rte_pci_device *dev)
> > >       FOREACH_DRIVER_ON_PCIBUS(dr) {
> > > +             if (dev->kdrv == RTE_KDRV_NONE)
> > > +                     continue;
> > >               rc = rte_pci_probe_one_driver(dr, dev);
> >
> > Nack
> 
> I understand mlx4/mlx5 is using RTE_KDRV_UNKNOWN, Here we are skipping
> the RTE_KDRV_NONE,
> What is the use case for probing the devices with RTE_KDRV_NONE?

Maybe you are right. I don't remember the use case.
I think I remember these virtio and vmxnet3 PMD were not using UIO:
	http://git.dpdk.org/old/virtio-net-pmd/tree/virtio_user.c
	http://git.dpdk.org/old/vmxnet3-usermap/tree/pmd/vmxnet3.c

We need to know which case is using following code:

    case RTE_KDRV_NONE:
#if defined(RTE_ARCH_X86)
        ret = pci_ioport_map(dev, bar, p);
#endif
        break;

David, please could you refresh our memory?