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On Thu, 2012-08-02 at 13:06 +0100, Harry van Haaren wrote:

quoted text
> Hi all,

>=20

>=20

> I've working on a LV2 instrument plugin, and it consumes about 1-2%

> CPU on idle. When I leave it for about 20 seconds, the CPU usage jumps

> to 38 / 40 % of a core, and JACK xruns. The code contains IIR's for a

> reverb effect, so I'm going to blame this CPU burning on denormal

> values.

>=20

>=20

> I'm using waf as the build system, and appending "-O3" and

> "-ffast-math" to the CFLAGS and CXXFLAGS. Building with ./waf -v shows

> the runner thread to have the "-O3" and "-ffast-math" in the command.

> Yet when I run it it still hogs CPU after about 10-20 seconds.

>=20

>=20

> Reading on gcc's pages

> (http://www.acsu.buffalo.edu/~charngda/cc.html) tells me that if

> DenomalsAreZero and FlushToZero are set, it should be linked with

> crtfastmath.o. I don't know how to check if this is happening?

>=20

>=20

> I'm not sure where to look next to fix the problem. Help appreciated!

Have you tried in Ardour, or another host with denormal protection?  I

know you were using Jalv recently, which does not.
On that note, a couple of denormal questions:
Is there a reason Jack can't do this for everything?  I am not really

keen on putting a bunch of mysterious assembler crap in a host meant to

be a relatively clean example, and it's even worse to make plugins have

to do this...
What is the scope of the state of the flush-to-zero flag?  Process?

Thread?
Thanks,
-dr
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