On 15.11.2013 21:17, Antti Palosaari wrote:
On 15.11.2013 21:13, Devin Heitmueller wrote:
On Fri, Nov 15, 2013 at 2:11 PM, Antti Palosaari <cr...@iki.fi> wrote:
When I do it inside Kernel, in URB completion handler at the same
time when
copying data to videobuf2, using pre-calculated LUTs and using mmap
it eats
0.5% CPU to transfer stream to app.
When I do same but using libv4lconvert as that patch, it takes ~11% CPU.
How are you measuring? Interrupt handlers typically don't count
toward the CPU performance counters. It's possible that the cost is
the same but you're just not seeing it in "top".
Yes, using top and it is URB interrupt handler where I do conversion. So
any idea how to measure? I think I can still switch LUT to float and see
if it makes difference.
I did some more tests. I added LUT to libv4lconvert and CPU usage of
process dropped to ~3.5%. It is very simple app that just feeds data
from device using mmap and conversion is done by libv4lconvert. Output
is feed to standard out which I dumped to /dev/null on tests.
So it is quite clear that runtime float conversion is CPU hungry when
conversion rate goes that high (up to 30M conversions per sec).
It is still not very much when compared to CPU needed for average signal
processing after that, but it will increase directly CPU usage of that
application. So is there idea to add threads for libv4lconvert in order
to get conversion out from application context ?
regards
Antti
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