Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size

From	Sinan Kaya <okaya@codeaurora.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size
Date	2017-09-20 17:10 +0200
Message-ID	<urONs-4IC-1@gated-at.bofh.it> (permalink)
References	(1 earlier) <uruYq-8tS-5@gated-at.bofh.it> <urxjA-1CN-15@gated-at.bofh.it> <urI5j-8tt-3@gated-at.bofh.it> <urMVk-3rX-17@gated-at.bofh.it> <urOaJ-4ey-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 9/20/2017 10:26 AM, Auger Eric wrote:
>> Because completions are required to be a minimum of MPS size. If MRRS > MPS,
>> read response is sent as multiple completions.
> With that patch, you can end up with MRRS < MPS. Do I understand
> correctly this is an issue?

To give the right context, I tried to mean that you can't use MRRS as a length
value for completions if MRRS is a fairly large number and bigger than MPS.

Therefore, a single completion packet size needs to be less than MRRS and cannot
exceed MPS. Spec is even calling for receivers to throw an error if completion
length is greater than MPS.

single completion <= MPS (128) <= MRRS (4k)

I looked at the spec again. I have not seen anything in the spec that prohibits
MRRS < MPS as long as completion size is less than MPS.

single completion <= MRRS (128) < MPS (256)

I think this is also valid. 

I hope I got it right this time.

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

Thread

[PATCH] vfio/pci: Virtualize Maximum Payload Size Alex Williamson <alex.williamson@redhat.com> - 2017-09-19 19:00 +0200
  Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Auger Eric <eric.auger@redhat.com> - 2017-09-19 20:00 +0200
    Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Alex Williamson <alex.williamson@redhat.com> - 2017-09-19 22:30 +0200
      Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Auger Eric <eric.auger@redhat.com> - 2017-09-20 10:00 +0200
        Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Sinan Kaya <okaya@codeaurora.org> - 2017-09-20 15:10 +0200
        Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Sinan Kaya <okaya@codeaurora.org> - 2017-09-20 15:10 +0200
          Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Auger Eric <eric.auger@redhat.com> - 2017-09-20 16:30 +0200
            Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Sinan Kaya <okaya@codeaurora.org> - 2017-09-20 17:10 +0200
            Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Alex Williamson <alex.williamson@redhat.com> - 2017-09-20 18:20 +0200
              Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Sinan Kaya <okaya@codeaurora.org> - 2017-09-20 18:30 +0200
                Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Auger Eric <eric.auger@redhat.com> - 2017-09-21 08:40 +0200
  Re: [PATCH] vfio/pci: Virtualize Maximum Payload Size Auger Eric <eric.auger@redhat.com> - 2017-09-21 08:40 +0200

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