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

[Zhou, Jammy]

Thanks Axel. It is consistent with my understanding. 

For the 'pixmap' check in your previous change, it is used to differentiate present_pixmap and present_notify_msc, right? It looks like "target_msc >= crtc_msc" was used at the first place for present_pixmap, do you know the background about this?

Regards,
Jammy

-----Original Message-----
From: Axel Davy [mailto:axel.davy at ens.fr] 
Sent: Monday, November 02, 2015 4:45 PM
To: Zhou, Jammy; Michel Dänzer
Cc: xorg-devel at lists.x.org; Mario Kleiner
Subject: Re: [PATCH] present: Execute right away if target_msc equals current_msc

Hi,

As you can see here:
http://cgit.freedesktop.org/xorg/proto/presentproto/tree/presentproto.txt#n212

It means to present immediately instead of waiting for the next vblank (if needed).

In practice when needed to present immediately, if the ddx is not able to do async flips, then we do a copy to the screen buffer, else we use that ability.

Yours,

Axel

On 02/11/2015 09:26, Zhou, Jammy wrote :
> 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>
>>
>>