[MPlayer-dev-eng] SFENCE really needed?

[Michael Niedermayer]

Hi

On Tuesday 21 January 2003 06:22, D Richard Felker III wrote:
> Hmm, I was reading some of the fast/agp memcpy code and other related
> stuff, and I'm wondering...what's the performance penalty for using
> the SFENCE instruction, and is it really necessary after writes to
> video memory? I could understand it being useful when writing to
> system memory, when another procedure might need to read the data
> after you write it. But from what I understand, it's nonsense when
> writing to video mem unless you plan on reading from video mem (slow
> and pointless!). Any ideas?
its needed, btw if u really dont read the data from there then why do u write 
it in the video mem? (hint the grafix card reads it & displays it on screen, 
so the last few pixels could be missing ..., i dunno if that would happen in 
practice, but it could IMHO according to the manuals) 

[...]

Michael