[MPlayer-dev-eng] [PATCH][RESEND] XV page flipping sync

[Joey Parrish]

Hello,

This mail has been sitting in my inbox for some time now.  There was no
[PATCH] in the subject, which may be why it's not committed.

The original mail is from Piotr Neuman <sikkh at wp.pl> on Mar 14.

> On my desktop machine (Athlon XP 2000+, Gigabyte VIA VT266a, Radeon 9000, 
> XFree 4.3, kernel 2.6.4-ck1) there were some problems in synchronization of 
> video output (XV driver) - I could see for example 'tearing' (when double 
> buffering was used).

> After some investigaton into it with help of Con Kolivas we were able to 
> conclude that on my kernel/hw configuration, there is priviledge inversion 
> issue (mplayer niced to +1 would work just fine). Such problems are usually 
> caused by how programs are written.

> It boils down to the usage of XFlush() in libvo/vo_xv.c . The problem is that 
> when synchronizing mplayer video buffer with X display, this function can't 
> ensure that X server will be given timeslice soon enough.

> Mplayer can continue rendering of next frame/frames (when page flipping is 
> used) after calling XFlush but X server may not be able to update screen on 
> time, so few pages may be 'lost' (flipped at wrong time intervals beetween 
> each other).

> My patch changes XFlush() call into XSync() which ensures that page will be 
> flipped properly on time (ie. when using -double switch), becose this call 
> waits till X has reported completion and gives free hand for system scheduler 
> to assing timeslice for X (thanks to blocking mplayer - preempting it).

> Performance degradation is neglible, according to my limited testing. For 
> example for Matrix mirage trailer (matrix_tr_mirage_480.mov) (sound output 
> thru alsa1x):

> before patching:
> BENCHMARKs: VC:  13,746s VO:   1,344s A:   0,954s Sys:  43,573s =   59,617s
> BENCHMARK%: VC: 23,0570% VO:  2,2551% A:  1,5997% Sys: 73,0882% = 100,0000%

> after:
> BENCHMARKs: VC:  11,691s VO:   4,802s A:   0,912s Sys:  42,216s =   59,621s
> BENCHMARK%: VC: 19,6089% VO:  8,0539% A:  1,5296% Sys: 70,8077% = 100,0000%

> With this change the output is synchronized very well, even though mplayer 
> uses usleep() timing (note that 2.6 kernels have clock set to 1000Hz, so 
> using rtc is uneceseary - A-V sync is ~ +- 0,005 at worst). The issue of 
> prority inversion is gone.

> The patch also contains removal of unneceseary calls to XFlush function just 
> before XSync is called (XSync() alone suffices).

> Regards.

> Piotr Neuman

I can't remember if anyone responded to this, but I saw some improvement
on my box.  But I don't know much about XV.  Any reason not to apply this?

--Joey

-- 
"There are trivial truths and there are great truths.  The opposite of a
trivial truth is plainly false.  The opposite of a great truth is also true."
  --Neils Bohr