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

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

> -----Original Message-----
> From: Neil Horman [mailto:nhorman@tuxdriver.com]
> Sent: Thursday, September 1, 2016 8:16 PM
> To: Stephen Hemminger <stephen@networkplumber.org>
> Cc: Trahe, Fiona <fiona.trahe@intel.com>; dev@dpdk.org; Olivier Matz
> <olivier.matz@6wind.com>; Thomas Monjalon
> <thomas.monjalon@6wind.com>
> Subject: Re: [dpdk-dev] [dpdk-dev, RFC] drivers: advertise kmod dependencies
> in pmdinfo
> 
> On Thu, Sep 01, 2016 at 10:41:22AM -0700, Stephen Hemminger wrote:
> > 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.

Actually if the script output was intended to be used to auto-load dependent kmods, 
then even the above would not suffice for the QAT driver (and presumably for other
PMDs with specific HW dependencies). i.e. the qat_dhxxxx modules have further dependencies 
themselves on an intel_qat module, and there are other steps documented in the 
guide which must be taken after loading the kmods. 
The use-case I'd addressed was for the script to identify and just throw an error where 
dependent modules are missing. 

I don't see a simple solution, but also don't see a strong need to find one. 
Documentation and if necessary a driver-specific script seem sufficient to me.

My conclusion is the RFC is a nice feature for some drivers, but if introduced needs 
to be optional as it doesn't handle the complexities of all drivers. 

> >
> > 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.
> >
> That sounds like a reasonable approach, yes.
> Neil
> 
> >