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

[Zhou, Jammy]

By the way, does PresentOptionAsync mean the same thing with the async flip capability in kernel side? Or is it just a flag to indicate X/DDX to do present immediately instead of waiting for the next vblank?

Regards,
Jammy

-----Original Message-----
From: Axel Davy [mailto:axel.davy at ens.fr] 
Sent: Thursday, October 29, 2015 3:42 PM
To: Michel Dänzer; Zhou, Jammy
Cc: xorg-devel at lists.x.org; Mario Kleiner
Subject: Re: [PATCH] present: Execute right away if target_msc equals current_msc

Hi,

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.

Yours,

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>
>
>