[FFmpeg-devel] flag naming conventions?

[Loren Merritt]

On Sat, 9 Mar 2013, "René J.V. Bertin" wrote:

> It ticks with the CPU frequency which is highly variable on modern CPUs.

True on some CPUs, not on others. On e.g. sandybridge, TSC follows the
base clockrate independent of which turbo boost setting is in use.

> Also, on systems with multiple TSCs (multi CPU or even mono-cpu, multi
> core systems), there is no way of knowing which of the ones you're
> reading at a given time (or at least that used to be the case).

Recent x86 have rdtscp, which does tell you which core you're on.
And even if the timers are synchronized, you still have to detect and
filter out samples that contain a context switch if you want to benchmark
your own code and not the OS. If you can do that, you'll catch any
instances of switching from one core to another without needing a special
case.

--Loren Merritt