[FFmpeg-devel] [PATCH] Improve handling of cmov usage enablement
Sat Nov 1 14:05:15 CET 2008
On Sat, Nov 01, 2008 at 01:52:02PM +0100, Dominik 'Rathann' Mierzejewski wrote:
> The attached patch enables CMOV by default on x86_64 arch, because
> all x86_64 CPUs have it. It doesn't enable fast_cmov, because x86_64
> includes some NetBurst-architecture CPUs from Intel, which are known
> to have a slow implementation of CMOV.
> The second part of the patch disables fast_cmov for the "i686" cpu
> target, because that target might include NetBurst-arch CPUs.
> OK to apply?
Given the statements by Intel I saw, my opinion is that we should go
with "enable fast_cmov unless we are really sure it is slow" - unless it
is some really predictable condition (in which case cmov probably is a
bad idea for all CPUs) cmov is likely to be faster on all CPUs except
netburst, including future CPUs.
Or in other words: Netburst is the special case, and our configure
should treat it as such, and personally my opinion is: you bought a
crappy CPU when everybody could have told you it is stupid (and going by
my experience a lot of people have told and been ignored), now live with
it, not our problem unless it is no effort for us. Complain to Intel if
More information about the ffmpeg-devel