[Mesa-dev] [PATCH 3/3] glx/dri3: Request non-vsynced Present for swapinterval zero.
Mario Kleiner
mario.kleiner.de at gmail.com
Sun Nov 30 03:47:16 PST 2014
On 11/25/2014 07:52 AM, Axel Davy wrote:
> Hi,
>
Sorry for the late reply, seems my e-mail filters hate me - i was
already worried about the lack of replies.
> This patch removes the tripple buffering behaviour that the GLX
> implementation
> has with DRI3. I understand your concern for Medical softwares,
> but perhaps this would be better handled with an user option.
>
> Axel Davy
>
I don't think it does that?
For swapinterval > 0 all the triple-buffering etc. is left active as
usual, and swaps are supposed to be vsynced and tear-free. swapinterval
is 1 by default, so this is the case by default.
For a client or user selected swapinterval = 0, the code in Mesa
schedules glXSwapBuffers calls to occur immediately, and the Present
implementation in the server schedules them in a way so they are
supposed to occur immediately/asap - assuming no vsync, otherwise the
logic there wouldn't make much sense.
Due to what i'm pretty sure is a bug (see my other 2 patches on top of
the xserver dri3/present implementation) the PresentOptionAsync isn't
handled correctly by the server for pagelfips as it should be, and as
result vsync is always on on intel-ddx, and always off on nouveau-ddx
(or any future driver which exposes PresentCapabilityAsync as nouveau
does), which causes massive tearing on nouveau all the time under
dri3/present.
On any os/graphics-stack i'm familiar with (Windows and OSX all versions
and drivers, Linux proprietary drivers, DRI2 with intel-ddx and
nouveau-ddx) a swapinterval zero meant to swap immediately without
vsync, so this just restores what probably any OpenGL client expects to
happen. The MESA_swap_control spec even states that "If <interval> is
set to a value of 0, buffer swaps are not synchronized to a video frame."
For medical or neuro-science applications like mine, or multi-display
stereo/VR applications it is crucial to have this for users being able
to easily diagnose multi-display synchronization issues without the need
to learn how to use git and compilers and how graphics stacks work. For
gamers and gaming benchmarks it's the "ego-shooter mode" and "squeeze
out max fps" they like so much.
Btw., digging deeper into the ddx'es i realized that my posted patch for
the x-server bug is both incomplete and too complex. I've written a new
patch which is only a simple one-liner but solves more problems than the
old one. I'll send it out after giving it some testing.
thanks,
-mario
> On 25/11/2014 04:00, Mario Kleiner wrote :
>> Restores proper immediate tearing swap behaviour for
>> OpenGL bufferswap under DRI3/Present.
>>
>> Cc: "10.3 10.4" <mesa-stable at lists.freedesktop.org>
>> Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
>> ---
>> src/glx/dri3_glx.c | 6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/glx/dri3_glx.c b/src/glx/dri3_glx.c
>> index 5796491..c53be1b 100644
>> --- a/src/glx/dri3_glx.c
>> +++ b/src/glx/dri3_glx.c
>> @@ -1518,6 +1518,7 @@ dri3_swap_buffers(__GLXDRIdrawable *pdraw,
>> int64_t target_msc, int64_t divisor,
>> xcb_connection_t *c = XGetXCBConnection(dpy);
>> struct dri3_buffer *back;
>> int64_t ret = 0;
>> + uint32_t options = XCB_PRESENT_OPTION_NONE;
>> unsigned flags = __DRI2_FLUSH_DRAWABLE;
>> if (flush)
>> @@ -1557,6 +1558,9 @@ dri3_swap_buffers(__GLXDRIdrawable *pdraw,
>> int64_t target_msc, int64_t divisor,
>> if (target_msc == 0)
>> target_msc = priv->msc + priv->swap_interval *
>> (priv->send_sbc - priv->recv_sbc);
>> + if (priv->swap_interval == 0)
>> + options |= XCB_PRESENT_OPTION_ASYNC;
>> +
>> back->busy = 1;
>> back->last_swap = priv->send_sbc;
>> xcb_present_pixmap(c,
>> @@ -1570,7 +1574,7 @@ dri3_swap_buffers(__GLXDRIdrawable *pdraw,
>> int64_t target_msc, int64_t divisor,
>> None, /* target_crtc */
>> None,
>> back->sync_fence,
>> - XCB_PRESENT_OPTION_NONE,
>> + options,
>> target_msc,
>> divisor,
>> remainder, 0, NULL);
>
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