[PATCH] present: Execute right away if target_msc equals current_msc

Axel Davy axel.davy at ens.fr
Thu Oct 29 00:41:42 PDT 2015


What is the current conscensus for how should PresentOptionAsync work ?

If I remember correctly, the semantic used to be:

. if we present at the current or past msc with the flag, two options:
-> if the ddx doesn't support async swap, we do copy to the screen 
pixmap right away
-> if the ddx does support it, we do an async swap right away

. if we present at another msc, things behave as without 
PresentOptionAsync, that is we schedule a swap,
and ask at msc-1 to the ddx to swap for msc.

With "Fix use of vsynced pageflips", I get the impression it shifted to:

. Async requested, but driver not having the async option -> do screen 
copy (no flips, whatever the msc)
. if Async not requested and flip planned, present at msc-1, else at 
msc. (so for flips and Async flag, we do always plan to flip at msc ? 
That means always tear, right ?)

That doesn't make a lot of sense to me, can someone clarify ?

I'm afraid this patch could be a workaround to currently broken 
behaviour, and not the correct fix.

I CCed Mario Kleiner.


Axel Davy

On 29/10/2015 03:53, Michel Dänzer wrote:
> On 28.10.2015 19:39, Jammy Zhou wrote:
>> It is according to the protocol:
>> "If 'options' contains PresentOptionAsync, and the 'target-msc'
>> is less than or equal to the current msc for 'window', then
>> the operation will be performed as soon as possible, not
>> necessarily waiting for the next vertical blank interval."
>> Signed-off-by: Jammy Zhou <Jammy.Zhou at amd.com>
>> ---
>>   present/present.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> diff --git a/present/present.c b/present/present.c
>> index beb4ff0..5900c22 100644
>> --- a/present/present.c
>> +++ b/present/present.c
>> @@ -871,7 +871,7 @@ present_pixmap(WindowPtr window,
>>       xorg_list_add(&vblank->event_queue, &present_exec_queue);
>>       vblank->queued = TRUE;
>> -    if ((pixmap && target_msc >= crtc_msc) || (!pixmap && target_msc > crtc_msc)) {
>> +    if (target_msc > crtc_msc) {
>>           ret = present_queue_vblank(screen, target_crtc, vblank->event_id, target_msc);
>>           if (ret == Success)
>>               return Success;
> Looks good to me, but Cc'ing Axel Davy, who made the last change to this
> code.
> Reviewed-by: Michel Dänzer <michel.daenzer at amd.com>

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