[MPlayer-dev-eng] SFENCE really needed?

[D Richard Felker III]

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?

Rich