Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf operations

From	Daniel Vetter <daniel@ffwll.ch>
Newsgroups	linux.kernel
Subject	Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf operations
Date	2017-06-29 10:40 +0200
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On Thu, Jun 29, 2017 at 08:41:53AM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > > Does gvt track the live cycle of all dma-bufs it has handed out?
> > 
> > The V9 implementation does track the dma-bufs' live cycle. The
> > original idea was that leaving the dma-bufs' live cycle management to
> > user mode.
> 
> That is still the case, user space decides which dma-bufs it'll go keep
> cached.  But kernel space can see what user space is doing, so there is
> no need to explicitly tell the kernel whenever a cached dma-buf exists
> or not.

We do the same trick in drm_prime.c, keeping a cache of exported dma-buf
around for re-exporting. Since for prime sharing the use-case is almost
always re-importing as a drm gem buffer again we can then on re-import
also tell userspace whether it already has that buffer in it's userspace
buffer manager, but that's an additional optimization. With plain dma-buf
we could achieve the same by wiring up a real stat() implementation with
unique inode numbers (atm they all share the anon_inode singleton). But
thus far no one asked for that.

btw I'm lost a bit in the discussion (was on vacation), but I think all
the concerns I've noticed with the initial rfc have been raised already,
so things look good. I'll check the next rfc once that shows up.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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RE: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf         operations "Zhang, Tina" <tina.zhang@intel.com> - 2017-06-20 10:50 +0200
  Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-20 13:00 +0200
    Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Alex Williamson <alex.williamson@redhat.com> - 2017-06-20 17:10 +0200
      Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Kirti Wankhede <kwankhede@nvidia.com> - 2017-06-20 19:10 +0200
      RE: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations "Zhang, Tina" <tina.zhang@intel.com> - 2017-06-21 01:10 +0200
        Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Alex Williamson <alex.williamson@redhat.com> - 2017-06-21 01:30 +0200
          RE: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations "Zhang, Tina" <tina.zhang@intel.com> - 2017-06-21 11:30 +0200
            Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-21 13:10 +0200
              Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Alex Williamson <alex.williamson@redhat.com> - 2017-06-21 21:00 +0200
                Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-22 10:40 +0200
                Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Alex Williamson <alex.williamson@redhat.com> - 2017-06-22 21:00 +0200
                Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-23 09:30 +0200
                Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf operations Zhi Wang <zhi.a.wang@intel.com> - 2017-06-23 10:10 +0200
                Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-23 10:40 +0200
                Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Alex Williamson <alex.williamson@redhat.com> - 2017-06-23 18:50 +0200
                Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Alex Williamson <alex.williamson@redhat.com> - 2017-06-23 19:20 +0200
                Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-26 08:20 +0200
              RE: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations "Zhang, Tina" <tina.zhang@intel.com> - 2017-06-22 02:30 +0200
      Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-21 09:40 +0200
    RE: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations "Zhang, Tina" <tina.zhang@intel.com> - 2017-06-24 00:00 +0200
      Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-26 08:40 +0200
        Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Alex Williamson <alex.williamson@redhat.com> - 2017-06-26 19:30 +0200
          Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-27 08:20 +0200
            RE: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations "Zhang, Tina" <tina.zhang@intel.com> - 2017-06-28 14:50 +0200
              Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Gerd Hoffmann <kraxel@redhat.com> - 2017-06-29 08:50 +0200
                Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf  operations Daniel Vetter <daniel@ffwll.ch> - 2017-06-29 10:40 +0200

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