Re: [PATCH] drm/i915: remove questionable fence optimization during copy

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Am 21.12.21 um 16:47 schrieb Thomas Hellström:
Hi, Christian,

On Tue, 2021-12-21 at 15:07 +0100, Christian König wrote:
First of all as discussed multiple times now kernel copies *must*
always wait
for all fences in a BO before actually doing the copy. This is
mandatory.
This patch looks ok to me.

Regarding the discussion I was just awaiting  Daniel's reply from
yesterday:

https://lists.freedesktop.org/archives/intel-gfx/2021-December/285717.html

since his earlier reply

https://lists.freedesktop.org/archives/intel-gfx/2021-December/285717.html

contradicted your previous reply

https://lists.freedesktop.org/archives/intel-gfx/2021-December/284467.html

That confirmed all writes had to add an exclusive fence, and confirmed
that starting the blit early was ok.

So I was left a bit confused as to what the rules really were.

So now if I understand both of you correctly, writers that want to opt
out of implicit syncing do *not* need to add an exclusive fence. Is
that correct?

Yes, that's a good summary of the problem.

Additional to that drop the handling when there can't be a shared
slot
allocated on the source BO and just properly return an error code.
Otherwise
this code path would only be tested under out of memory conditions.
Good point.

Signed-off-by: Christian König <christian.koenig@xxxxxxx>
Reviewed-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>

Ok if I add this to drm-intel-gt-next?

Please go ahead.

Thanks,
Christian.


/Thomas






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