[FFmpeg-user] Not using all resources

Andy Furniss adf.lists at gmail.com
Tue Sep 8 02:10:37 CEST 2015

Henk D. Schoneveld wrote:
> Hi all,
> I’m encoding from several DVB-S sources, satellite, with always the
> same parameters but recordings from some sources CPU-load is about
> 50% of what it could be, others use max. available as attachments
> show.
> The 1st inserts a srt file while the 2nd doesn’t but because there’s
> no IO-bottleneck that should be a problem I think.
> Any idea what could be the cause of it ? It’s not really problematic,
> just curious.

May not apply in this case/your CPU but -

Cpufreq on_demand is sometimes stupid and top doesn't always show the
full picture especially if simd is involved (may depend on h/w) and I
guess if cpufreq on_demand is in use % figures are meaningless without
polling the current frequency anyway (accepting that if they are > 90%
freq should have risen).

It could be my observations are just because I have an old AMD Phenom -
but I once came across an old ffmpeg-devel post where some one made some
C version of CSC code that beat the SIMD ASM. Shame it was old or I
could have posted - yes I see exactly the same - but that's because
cpufreq on_demand doesn't kick in in the SIMD case - set the CPUs to
perf and the SIMD will beat the C.

Above just to illustrate that "just looking" with top could mislead -
not saying it does for you, but always when benchmarking/measuring
consider setting CPUs to perf.

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