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

["Trahe, Fiona" <fiona.trahe@intel.com>]

Hi Neil and Olivier,

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Olivier Matz
> Sent: Wednesday, August 31, 2016 2:40 PM
> To: Neil Horman <nhorman@tuxdriver.com>
> Cc: dev@dpdk.org; thomas.monjalon@6wind.com
> Subject: Re: [dpdk-dev] [dpdk-dev, RFC] drivers: advertise kmod dependencies
> in pmdinfo
> 
> Hi Neil,
> 
> On 08/31/2016 03:27 PM, Neil Horman wrote:
> > 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.
> 
> Yep, that's the idea.
> 
> Colon and commas are the best separators I've thought about, but any
> idea to make the syntax clearer is welcome ;)
> 
> Maybe a syntax like is clearer:
>   "(mod1 & mod2)|(mod3 & mod4)" ?
> But it would let the user think that more complex expressions are valid,
> like "(mod1 & (mod2 | mod3)) | mod4", which is probably overkill.
> 
> Regards,
> Olivier

This RFC seems like a good idea - and something the Intel QuickAssist PMD could benefit from.
However the (mod1 & mod2) can handle the QAT case better in my opinion.
i.e.
as well as needing one of 
* uio igb_uio
* uio uio_pci_generic
* vfio vfio-pci
QAT PMD also needs one of (depending on which physical device is plugged)
 * qat_dh895xcc
 * qat_c62x
 * qat_c3xxx

So the original syntax would result in a very long list of possible variations.
What really reflects the dependencies would be 
((uio & igb_uio) | (uio & uio_pci_generic) | (vfio & vfio_pci)) & (qat_dh895xcc | qat_c62x | qat_c3xxx)

Also the dependencies on a VM are different to a bare-metal installation, i.e. the qat_xxxx driver just 
needs to be loaded in the Host. So maybe this could be satisfied by a separate list?
DRIVER_REGISTER_KMOD_DEP()
DRIVER_REGISTER_KMOD_VM_DEP()

But maybe this is all too complex, and instead the feature should be considered as optional and 
not requiring all dependencies to be declared? 

Regards,
Fiona