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

From	Vlad Zolotarov <vladz@cloudius-systems.com>
Newsgroups	linux.kernel
Subject	Re: [dpdk-dev] [PATCH 0/2] uio_msi: device driver
Date	2015-10-04 19:00 +0200
Message-ID	<qfUNH-68K-1@gated-at.bofh.it> (permalink)
References	(5 earlier) <qeV97-2d3-13@gated-at.bofh.it> <qeVCa-2KR-17@gated-at.bofh.it> <qeVLQ-2W2-7@gated-at.bofh.it> <qeW5b-3xz-3@gated-at.bofh.it> <qeXui-5r2-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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FYI: I've just posted to linux-kernel list patches that add support for 
both MSI and MSI-X interrupt modes to uio_pci_generic driver.
It addresses most (all) remarks on this thread and also fixes some 
issues this code has, e.g. not disabling msi-x in remove(), etc.

U are all welcome to comment... ;)

thanks,
vlad

On 10/02/15 04:39, Alexander Duyck wrote:
> On 10/01/2015 05:04 PM, Stephen Hemminger wrote:
>> On Thu, 1 Oct 2015 16:43:23 -0700
>> Alexander Duyck <alexander.duyck@gmail.com> wrote:
>>
>>> Yes, but in the case of something like a VF it is going to just make a
>>> bigger mess of things since INTx doesn't work.  So what would you 
>>> expect
>>> your driver to do in that case?  Also we have to keep in mind that the
>>> MSI-X failure case is very unlikely.
>>>
>>> One other thing that just occurred to me is that you may want to try
>>> using the range allocation call instead of a hard set number of
>>> interrupts.  Then if you start running short on vectors you don't hard
>>> fail and instead just allocate what you can.
>> I tried that but the bookkeeping gets messy since there is no good
>> way to communicate that back to userspace and have it adapt.
>
> Actually I kind of just realized that uio_msi_open is kind of messed 
> up.  So if the MSI-X allocation fails due to no resources it will 
> return a positive value indicating the number of vectors that could be 
> allocated, a negative value if one of the input values is invalid, or 
> 0.  I'm not sure if returning a positive value on failure is an issue 
> or not.  I know the open call is supposed to return a negative value 
> or the file descriptor if not negative.  I don't know if the return 
> value might be interpreted as a file descriptor or not.
>
> Also if MSI-X is supported by the hardware, but disabled for some 
> reason by the kernel ("pci=nomsi")  then this driver is rendered 
> inoperable since it will never give you anything but -EINVAL from the 
> open call.
>
> I really think you should probably look at taking care of enabling 
> MSI-X and maybe MSI as a fall-back in probe.  At least then you can 
> post a message about how many vectors are enabled and what type. Then 
> if you cannot enable any interrupts due to MSI being disabled you can 
> simply fail at probe time and let then load a different driver.
>
> - Alex

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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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