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

[Zhang, Tina]

> -----Original Message-----
> From: intel-gvt-dev [mailto:intel-gvt-dev-bounces@xxxxxxxxxxxxxxxxxxxxx] On
> Behalf Of Daniel Vetter
> Sent: Thursday, June 29, 2017 4:39 PM
> To: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> Cc: Wang, Zhenyu Z <zhenyu.z.wang@xxxxxxxxx>; intel-
> gfx@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Chen, Xiaoguang
> <xiaoguang.chen@xxxxxxxxx>; Zhang, Tina <tina.zhang@xxxxxxxxx>; Alex
> Williamson <alex.williamson@xxxxxxxxxx>; Lv, Zhiyuan
> <zhiyuan.lv@xxxxxxxxx>; Kirti Wankhede <kwankhede@xxxxxxxxxx>; intel-gvt-
> dev@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf
> operations
> 
> 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.

Thanks. I'm going to submit the v10 version of ABI interface.

> 
> 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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