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

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 1 Sep 2016 13:35:19 -0400
Neil Horman <nhorman@tuxdriver.com> wrote:

> On Thu, Sep 01, 2016 at 12:55:27PM +0000, Trahe, Fiona wrote:
> > 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)
> >   
> Ah, I didn't consider that hardware specifics might create a use case where a
> pmd must have one or more kernel modules available for hw support.  Perhaps it
> is worthwhile to automate hardware support - that is to say, any module loading
> script should automatically look at the pci table exported from a pmd, and, if
> found, load any modules that claim support for that device:vendor tuple?  Though
> that might break in the case of uio, if there are separate driver modules that
> support native hardware and uio access.

I ended up writing a script that went the other way.
First look at the hardware and load VFIO if IOMMU is available.
Then look for special driver needed for Xen and HyperV
Lastly fallback to loading igb_uio if no VFIO and PCI device present.

In other words it is a system not driver issue.