Re: [PATCH v6 10/14] drm/panthor: Add the scheduler logical block

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue, 3 Sep 2024 21:43:48 +0200
Simona Vetter <simona.vetter@ffwll.ch> wrote:

> On Thu, Feb 29, 2024 at 05:22:24PM +0100, Boris Brezillon wrote:
> > - Add our job fence as DMA_RESV_USAGE_WRITE to all external objects
> >   (was previously DMA_RESV_USAGE_BOOKKEEP). I don't get why, given
> >   we're supposed to be fully-explicit, but other drivers do that, so
> >   there must be a good reason  
> 
> Just spotted this: They're wrong, or they're userspace is broken and
> doesn't use the dma_buf fence import/export ioctl in all the right places.
> For gl this simplifies things (but setting write fences when you're only
> reading is still bad, and setting fences on buffers you don't even touch
> is worse), for vulkan this is just bad.

For the record, I remember pointing that out in some drm_sched
discussion, and being told that this was done on purpose :-/.

> 
> I think you want a context creation flag for userspace that's not broken,
> which goes back to USAGE_BOOKKEEP for everything.

Honestly, given the only user (the gallium driver) is already designed
to do the explicit <-> implicit dance, and the fact the driver just got
merged in the last release, I'd rather go for a silent USAGE_WRITE ->
USAGE_BOOKKEEP if things keep working with that.