Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver

From	Stephen Hemminger <stephen@networkplumber.org>
Newsgroups	linux.kernel
Subject	Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver
Date	2015-10-02 01:40 +0200
Message-ID	<qeVCa-2KR-17@gated-at.bofh.it> (permalink)
References	(1 earlier) <qeJKG-1N3-9@gated-at.bofh.it> <qeNuX-7IQ-23@gated-at.bofh.it> <qeS1z-5PY-7@gated-at.bofh.it> <qeUd4-Rt-25@gated-at.bofh.it> <qeV97-2d3-13@gated-at.bofh.it>
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On Thu, 1 Oct 2015 16:03:06 -0700
Alexander Duyck <alexander.duyck@gmail.com> wrote:

> On 10/01/2015 03:00 PM, Stephen Hemminger wrote:
> > On Thu, 1 Oct 2015 12:48:36 -0700
> > Alexander Duyck <alexander.duyck@gmail.com> wrote:
> >
> >> On 10/01/2015 07:57 AM, Stephen Hemminger wrote:
> >>> On Thu, 1 Oct 2015 13:59:02 +0300
> >>> Avi Kivity <avi@scylladb.com> wrote:
> >>>
> >>>> On 10/01/2015 01:28 AM, Stephen Hemminger wrote:
> >>>>> This is a new UIO device driver to allow supporting MSI-X and MSI devices
> >>>>> in userspace.  It has been used in environments like VMware and older versions
> >>>>> of QEMU/KVM where no IOMMU support is available.
> >>>> Why not add msi/msix support to uio_pci_generic?
> >>> That is possible but that would meet ABI and other resistance from the author.
> >>> Also, uio_pci_generic makes it harder to find resources since it doesn't fully
> >>> utilize UIO infrastructure.
> >> I'd say you are better off actually taking this in the other direction.
> >>  From what I have seen it seems like this driver is meant to deal with
> >> mapping VFs contained inside of guests.  If you are going to fork off
> >> and create a UIO driver for mapping VFs why not just make it specialize
> >> in that.  You could probably simplify the code by dropping support for
> >> legacy interrupts and IO regions since all that is already covered by
> >> uio_pci_generic anyway if I am not mistaken.
> >>
> >> You could then look at naming it something like uio_vf since the uio_msi
> >> is a bit of a misnomer since it is MSI-X it supports, not MSI interrupts.
> > The support needs to cover:
> >    - VF in guest
> >    - VNIC in guest (vmxnet3)
> > it isn't just about VF's
> 
> I get that, but the driver you are talking about adding is duplicating 
> much of what is already there in uio_pci_generic.  If nothing else it 
> might be worth while to look at replacing the legacy interrupt with 
> MSI.  Maybe look at naming it something like uio_pcie to indicate that 
> we are focusing on assigning PCIe and virtual devices that support MSI 
> and MSI-X and use memory BARs rather than legacy PCI devices that are 
> doing things like mapping I/O BARs and using INTx signaling.
> 
> My main argument is that we should probably look at dropping support for 
> anything that isn't going to be needed.  If it is really important we 
> can always add it later.  I just don't see the value in having code 
> around for things we aren't likely to ever use with real devices as we 
> are stuck supporting it for the life of the driver. I'll go ahead and 
> provide a inline review of your patch 2/2 as I think my feedback might 
> make a bit more sense that way.

Ok, but having one driver that can deal with failures with msi-x vector
setup and fallback seemed like a better strategy.


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Thread

[PATCH 0/2] uio_msi: device driver Stephen Hemminger <stephen@networkplumber.org> - 2015-10-01 00:30 +0200
  [PATCH 2/2] uio: new driver to support PCI MSI-X Stephen Hemminger <stephen@networkplumber.org> - 2015-10-01 00:30 +0200
    Re: [PATCH 2/2] uio: new driver to support PCI MSI-X "Michael S. Tsirkin" <mst@redhat.com> - 2015-10-01 10:40 +0200
      Re: [PATCH 2/2] uio: new driver to support PCI MSI-X "Michael S. Tsirkin" <mst@redhat.com> - 2015-10-01 12:40 +0200
        Re: [PATCH 2/2] uio: new driver to support PCI MSI-X "Michael S. Tsirkin" <mst@redhat.com> - 2015-10-01 18:10 +0200
      Re: [PATCH 2/2] uio: new driver to support PCI MSI-X Stephen Hemminger <stephen@networkplumber.org> - 2015-10-01 17:00 +0200
        Re: [PATCH 2/2] uio: new driver to support PCI MSI-X "Michael S. Tsirkin" <mst@redhat.com> - 2015-10-01 17:30 +0200
      Re: [PATCH 2/2] uio: new driver to support PCI MSI-X "Michael S. Tsirkin" <mst@redhat.com> - 2015-10-01 18:40 +0200
        Re: [PATCH 2/2] uio: new driver to support PCI MSI-X Stephen Hemminger <stephen@networkplumber.org> - 2015-10-01 19:30 +0200
          Re: [PATCH 2/2] uio: new driver to support PCI MSI-X "Michael S. Tsirkin" <mst@redhat.com> - 2015-10-01 20:30 +0200
      Re: [PATCH 2/2] uio: new driver to support PCI MSI-X "Michael S. Tsirkin" <mst@redhat.com> - 2015-10-06 00:00 +0200
    Re: [dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-02 01:50 +0200
      Re: [dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X Stephen Hemminger <stephen@networkplumber.org> - 2015-10-02 02:10 +0200
        Re: [dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-02 04:40 +0200
      Re: [dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X Stephen Hemminger <stephen@networkplumber.org> - 2015-10-02 02:10 +0200
        Re: [dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-02 03:30 +0200
  [PATCH 1/2] uio: add support for ioctls Stephen Hemminger <stephen@networkplumber.org> - 2015-10-01 00:30 +0200
  Re: [PATCH 0/2] uio_msi: device driver "Michael S. Tsirkin" <mst@redhat.com> - 2015-10-01 10:40 +0200
  Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Avi Kivity <avi@scylladb.com> - 2015-10-01 13:00 +0200
    Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Stephen Hemminger <stephen@networkplumber.org> - 2015-10-01 17:00 +0200
      Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-01 21:50 +0200
        Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Stephen Hemminger <stephen@networkplumber.org> - 2015-10-02 00:10 +0200
          Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-02 01:10 +0200
            Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Stephen Hemminger <stephen@networkplumber.org> - 2015-10-02 01:40 +0200
              Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-02 01:50 +0200
                Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Stephen Hemminger <stephen@networkplumber.org> - 2015-10-02 02:10 +0200
                Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-02 03:40 +0200
                Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Vlad Zolotarov <vladz@cloudius-systems.com> - 2015-10-04 19:00 +0200
                Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Greg KH <gregkh@linux-foundation.org> - 2015-10-04 21:10 +0200
                Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver Vlad Zolotarov <vladz@cloudius-systems.com> - 2015-10-04 22:50 +0200

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