Re: [dpdk-dev] [dpdk-dev, RFC] drivers: advertise kmod dependencies in pmdinfo

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, Aug 31, 2016 at 11:21:18AM +0200, Olivier Matz wrote:
> Hi Neil,
> 
> On 08/30/2016 03:23 PM, Neil Horman wrote:
> > On Fri, Aug 26, 2016 at 03:20:46PM +0200, Olivier Matz wrote:
> >> Add a new macro DRIVER_REGISTER_KMOD_DEP() that allows a driver to
> >> declare the list of kernel modules required to run properly.
> >>
> >> Today, most PCI drivers require uio/vfio.
> >>
> >> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> >>
> >> ---
> >> In this RFC, I supposed that all PCI drivers require a the loading of a
> >> uio/vfio module (except mlx*), this may be wrong.
> >> Comments are welcome!
> >>
> >>
> >>  buildtools/pmdinfogen/pmdinfogen.c      |  1 +
> >>  buildtools/pmdinfogen/pmdinfogen.h      |  1 +
> >>  drivers/crypto/qat/rte_qat_cryptodev.c  |  2 ++
> >>  drivers/net/bnx2x/bnx2x_ethdev.c        |  4 ++++
> >>  drivers/net/bnxt/bnxt_ethdev.c          |  2 ++
> >>  drivers/net/cxgbe/cxgbe_ethdev.c        |  2 ++
> >>  drivers/net/e1000/em_ethdev.c           |  2 ++
> >>  drivers/net/e1000/igb_ethdev.c          |  4 ++++
> >>  drivers/net/ena/ena_ethdev.c            |  2 ++
> >>  drivers/net/enic/enic_ethdev.c          |  2 ++
> >>  drivers/net/fm10k/fm10k_ethdev.c        |  2 ++
> >>  drivers/net/i40e/i40e_ethdev.c          |  2 ++
> >>  drivers/net/i40e/i40e_ethdev_vf.c       |  2 ++
> >>  drivers/net/ixgbe/ixgbe_ethdev.c        |  4 ++++
> >>  drivers/net/mlx4/mlx4.c                 |  2 ++
> >>  drivers/net/mlx5/mlx5.c                 |  3 +++
> >>  drivers/net/nfp/nfp_net.c               |  2 ++
> >>  drivers/net/qede/qede_ethdev.c          |  4 ++++
> >>  drivers/net/szedata2/rte_eth_szedata2.c |  2 ++
> >>  drivers/net/thunderx/nicvf_ethdev.c     |  2 ++
> >>  drivers/net/virtio/virtio_ethdev.c      |  2 ++
> >>  drivers/net/vmxnet3/vmxnet3_ethdev.c    |  2 ++
> >>  lib/librte_eal/common/include/rte_dev.h | 14 ++++++++++++++
> >>  tools/dpdk-pmdinfo.py                   |  5 ++++-
> >>  24 files changed, 69 insertions(+), 1 deletion(-)
> >>
> > 
> > Generally speaking, I like the idea, it makes sense to me in terms of using
> > pmdinfo to export this information
> > 
> > That said, This may need to be a set of macros.  By that I mean (and correct me
> > if I'm wrong here), but the relationship between pmd's and kernel modules is in
> > some cases, more complex than a 'requires' or 'depends' relationship.  That is
> > to say, some pmd may need user space hardware access, but can use either uio OR
> > vfio, but doesn't need both, and can continue to function if only one is
> > available.  Other PMD's may be able to use vfio or uio, but can still function
> > without either.  And some, as your patch implements, simply require one or the
> > other to function.  As such it seems like you may want a few macros, in the form
> > of:
> > 
> > DRIVER_REGISTER_KMOD_REQUEST - List of modules to attempt loading, ignore any
> > failures 
> > DRIVER_REGISTER_KMOD_REQUIRE - List of modules required to be loaded after
> > request macro completes, fail if any are not loaded
> > 
> > Thats just spitballing, mind you, theres probably a better way to do it, but the
> > idea is to list a set of modules you would like to have, and then create a
> > parsable syntax to describe the modules that need to be loaded after the request
> > is complete so that you can accurately codify the situations I described above.
> 
> Thank you for your feedback.
> However, I'm not sure I'm perfectly getting what you suggest.
> 
> Do you think some PMDs could request a kernel module without really
> requiring it? Do you have an example in mind?
> 
Yes, thats precisely it.  The most clear example I could think of (though I'm
not sure if any pmd currently supports this), is a pmd that supports both UIO
and VFIO communication with the kernel.  Such a PMD requires that one of those
two modules be loaded, but only one (i.e. both are not required), so if only the
uio kernel module loads is a success case, likewise if only the vfio module
loads can be treated as success.  Both loading are clearly successful.  Only if
neither load do we have a failure case.  I'm suggesting that the grammer that
your exports define should take those cases into account.  Its not always as
simple as "I must have the following modules"

> The syntax I've submitted lets you define several lists of modules, so
> that the user or the script that starts the application can decide which
> kmod list is better according to the environment.
> 
If you have a human intervening in the module load process, sure, then its fine.
But it seems that this particular feature that you're implemnting might have
automated uses.  That is to say the dpdk core library might be interested in
parsing this particular information to direct module autoloading, and if thats
desireable then you need to define these lists such that you can codify failure
and success conditions.

> For example, most drivers will advertise
> "uio,igb_uio:uio,uio_pci_generic:vfio,vfio-pci", and the user or script
> will have to choose between loading:
> - uio igb_uio
> - uio uio_pci_generic
> - vfio vfio-pci
> 
Oh, I see, so your list is a colon delimited list of module load sets, where at
least one set must succeed by loading all modules in its set, but the failure of
any one set isn't fatal to the process?  e.g. a string like this:

uio,igb_uio:vfio,vfio-pci

could be interpreted to mean "I must load (uio AND igb_uio) OR (vfio AND
vfio-pci).  If the evaluation of that statement results in false, then the
operation fails, otherwise it succedes.

If thats the case, then, apologies, we're on the same page, and this will work
just fine.

Best
Neil


> 
> Olivier
>