Re: [PATCH v2 0/2] drm/xe: flush engine buffers before signalling user fence on all engines

[Andrzej Hajda <andrzej.hajda@intel.com>]

On 04.06.2024 13:07, Thomas Hellström wrote:
> On Tue, 2024-06-04 at 11:38 +0200, Andrzej Hajda wrote:
>> According to the discussion result on my previous patch I have
>> prepared
>> new patchset, which reverts previous patch and adds barrier before
>> user fence signalling.
>> Remarks:
>> - I was not able to test it yet, hopefully CI will do it and me also
>> after fixing LNL issue,

Finally I can confirm that on LNL this patchset the barrier is enough, 
at least on the igt tests I was fixing.

>> - I am not sure about MI_FLUSH_DW flags, bspec says:
>>    "After this command is completed with a Store DWord enabled, CPU
>> access to graphics memory will be coherent"
>>    Shouldn't we use "Store DWord" then?
> It's not impossible that "store dword" needs to be enabled to act as a
> write barrier. but it also says "The parser pauses on an internal flush
> until all drawing engines have completed any pending operations."
>
> If it turns out a store dword is indeed needed as a post sync
> operation, we could perhaps use the "store dword" functionality of this
> command to store the user-fence value and replace the posted write.

Yep this seems even more elegant solution for me, but as I stated above 
the current solution works well.

Regards
Andrzej

>
> /Thomas
>
>> [1]:
>> https://lore.kernel.org/intel-xe/Zl5DcuZeZiFgxVdJ@DUT025-TGLU.fm.intel.com/T/#m0b4420045908bac70426728d460108c0b2b65dca
>>
>> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
>> ---
>> - Link to v1:
>> https://lore.kernel.org/r/20240603-fix_user_fence_posted-v1-1-61c76ef69cea@intel.com
>>
>> ---
>> Andrzej Hajda (2):
>>        Revert "drm/xe: flush gtt before signalling user fence on all
>> engines"
>>        drm/xe: flush engine buffers before signalling user fence on
>> all engines
>>
>>   drivers/gpu/drm/xe/xe_ring_ops.c | 26 ++++++++++++++++++++------
>>   1 file changed, 20 insertions(+), 6 deletions(-)
>> ---
>> base-commit: fe3d637a9c72b22297da0c731fa5e217bd182d2d
>> change-id: 20240603-fix_user_fence_posted-ca56c79c0662
>>
>> Best regards,